text: """Abstract syntax tree node classes (i.e. parse tree)."""
  
  import os
  from abc import abstractmethod
  from mypy.ordered_dict import OrderedDict
  from collections import defaultdict
  from typing import (
      Any, TypeVar, List, Tuple, cast, Set, Dict, Union, Optional, Callable, Sequence, Iterator
  )
  from typing_extensions import DefaultDict, Final, TYPE_CHECKING
  from mypy_extensions import trait
  
  import mypy.strconv
  from mypy.util import short_type
  from mypy.visitor import NodeVisitor, StatementVisitor, ExpressionVisitor
  
  from mypy.bogus_type import Bogus
  
  
  class Context:
      """Base type for objects that are valid as error message locations."""
      __slots__ = ('line', 'column', 'end_line')
  
      def __init__(self, line: int = -1, column: int = -1) -> None:
          self.line = line
          self.column = column
          self.end_line = None  # type: Optional[int]
  
      def set_line(self,
                   target: Union['Context', int],
                   column: Optional[int] = None,
                   end_line: Optional[int] = None) -> None:
          """If target is a node, pull line (and column) information
          into this node. If column is specified, this will override any column
          information coming from a node.
          """
          if isinstance(target, int):
              self.line = target
          else:
              self.line = target.line
              self.column = target.column
              self.end_line = target.end_line
  
          if column is not None:
              self.column = column
  
          if end_line is not None:
              self.end_line = end_line
  
      def get_line(self) -> int:
          """Don't use. Use x.line."""
          return self.line
  
      def get_column(self) -> int:
          """Don't use. Use x.column."""
          return self.column
  
  
  if TYPE_CHECKING:
      # break import cycle only needed for mypy
      import mypy.types
  
  
  T = TypeVar('T')
  
  JsonDict = Dict[str, Any]
  
  
  # Symbol table node kinds
  #
  # TODO rename to use more descriptive names
  
  LDEF = 0  # type: Final[int]
  GDEF = 1  # type: Final[int]
  MDEF = 2  # type: Final[int]
  
  # Placeholder for a name imported via 'from ... import'. Second phase of
  # semantic will replace this the actual imported reference. This is
  # needed so that we can detect whether a name has been imported during
  # XXX what?
  UNBOUND_IMPORTED = 3  # type: Final[int]
  
  # RevealExpr node kinds
  REVEAL_TYPE = 0  # type: Final[int]
  REVEAL_LOCALS = 1  # type: Final[int]
  
  LITERAL_YES = 2  # type: Final
  LITERAL_TYPE = 1  # type: Final
  LITERAL_NO = 0  # type: Final
  
  node_kinds = {
      LDEF: 'Ldef',
      GDEF: 'Gdef',
      MDEF: 'Mdef',
      UNBOUND_IMPORTED: 'UnboundImported',
  }  # type: Final
  inverse_node_kinds = {_kind: _name for _name, _kind in node_kinds.items()}  # type: Final
  
  
  implicit_module_attrs = {'__name__': '__builtins__.str',
                           '__doc__': None,  # depends on Python version, see semanal.py
                           '__file__': '__builtins__.str',
                           '__package__': '__builtins__.str'}  # type: Final
  
  
  # These aliases exist because built-in class objects are not subscriptable.
  # For example `list[int]` fails at runtime. Instead List[int] should be used.
  type_aliases = {
      'typing.List': 'builtins.list',
      'typing.Dict': 'builtins.dict',
      'typing.Set': 'builtins.set',
      'typing.FrozenSet': 'builtins.frozenset',
      'typing.ChainMap': 'collections.ChainMap',
      'typing.Counter': 'collections.Counter',
      'typing.DefaultDict': 'collections.defaultdict',
      'typing.Deque': 'collections.deque',
      'typing.OrderedDict': 'collections.OrderedDict',
  }  # type: Final
  
  # This keeps track of the oldest supported Python version where the corresponding
  # alias source is available.
  type_aliases_source_versions = {
      'typing.List': (2, 7),
      'typing.Dict': (2, 7),
      'typing.Set': (2, 7),
      'typing.FrozenSet': (2, 7),
      'typing.ChainMap': (3, 3),
      'typing.Counter': (2, 7),
      'typing.DefaultDict': (2, 7),
      'typing.Deque': (2, 7),
      'typing.OrderedDict': (3, 7),
  }  # type: Final
  
  reverse_builtin_aliases = {
      'builtins.list': 'typing.List',
      'builtins.dict': 'typing.Dict',
      'builtins.set': 'typing.Set',
      'builtins.frozenset': 'typing.FrozenSet',
  }  # type: Final
  
  nongen_builtins = {'builtins.tuple': 'typing.Tuple',
                     'builtins.enumerate': ''}  # type: Final
  nongen_builtins.update((name, alias) for alias, name in type_aliases.items())
  # Drop OrderedDict from this for backward compatibility
  del nongen_builtins['collections.OrderedDict']
  
  RUNTIME_PROTOCOL_DECOS = ('typing.runtime_checkable',
                            'typing_extensions.runtime',
                            'typing_extensions.runtime_checkable')  # type: Final
  
  
  class Node(Context):
      """Common base class for all non-type parse tree nodes."""
  
      __slots__ = ()
  
      def __str__(self) -> str:
          ans = self.accept(mypy.strconv.StrConv())
          if ans is None:
              return repr(self)
          return ans
  
      def accept(self, visitor: NodeVisitor[T]) -> T:
          raise RuntimeError('Not implemented')
  
  
  @trait
  class Statement(Node):
      """A statement node."""
  
      __slots__ = ()
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          raise RuntimeError('Not implemented')
  
  
  @trait
  class Expression(Node):
      """An expression node."""
  
      __slots__ = ()
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          raise RuntimeError('Not implemented')
  
  
  class FakeExpression(Expression):
      """A dummy expression.
  
      We need a dummy expression in one place, and can't instantiate Expression
      because it is a trait and mypyc barfs.
      """
      pass
  
  
  # TODO:
  # Lvalue = Union['NameExpr', 'MemberExpr', 'IndexExpr', 'SuperExpr', 'StarExpr'
  #                'TupleExpr']; see #1783.
  Lvalue = Expression
  
  
  @trait
  class SymbolNode(Node):
      """Nodes that can be stored in a symbol table."""
  
      __slots__ = ()
  
      @property
      @abstractmethod
      def name(self) -> str: pass
  
      # fullname can often be None even though the type system
      # disagrees. We mark this with Bogus to let mypyc know not to
      # worry about it.
      @property
      @abstractmethod
      def fullname(self) -> Bogus[str]: pass
  
      @abstractmethod
      def serialize(self) -> JsonDict: pass
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'SymbolNode':
          classname = data['.class']
          method = deserialize_map.get(classname)
          if method is not None:
              return method(data)
          raise NotImplementedError('unexpected .class {}'.format(classname))
  
  
  # Items: fullname, related symbol table node, surrounding type (if any)
  Definition = Tuple[str, 'SymbolTableNode', Optional['TypeInfo']]
  
  
  class MypyFile(SymbolNode):
      """The abstract syntax tree of a single source file."""
  
      # Fully qualified module name
      _fullname = None  # type: Bogus[str]
      # Path to the file (empty string if not known)
      path = ''
      # Top-level definitions and statements
      defs = None  # type: List[Statement]
      # Type alias dependencies as mapping from target to set of alias full names
      alias_deps = None  # type: DefaultDict[str, Set[str]]
      # Is there a UTF-8 BOM at the start?
      is_bom = False
      names = None  # type: SymbolTable
      # All import nodes within the file (also ones within functions etc.)
      imports = None  # type: List[ImportBase]
      # Lines on which to ignore certain errors when checking.
      # If the value is empty, ignore all errors; otherwise, the list contains all
      # error codes to ignore.
      ignored_lines = None  # type: Dict[int, List[str]]
      # Is this file represented by a stub file (.pyi)?
      is_stub = False
      # Is this loaded from the cache and thus missing the actual body of the file?
      is_cache_skeleton = False
      # Does this represent an __init__.pyi stub with a module __getattr__
      # (i.e. a partial stub package), for such packages we suppress any missing
      # module errors in addition to missing attribute errors.
      is_partial_stub_package = False
      # Plugin-created dependencies
      plugin_deps = None  # type: Dict[str, Set[str]]
  
      def __init__(self,
                   defs: List[Statement],
                   imports: List['ImportBase'],
                   is_bom: bool = False,
                   ignored_lines: Optional[Dict[int, List[str]]] = None) -> None:
          super().__init__()
          self.defs = defs
          self.line = 1  # Dummy line number
          self.imports = imports
          self.is_bom = is_bom
          self.alias_deps = defaultdict(set)
          self.plugin_deps = {}
          if ignored_lines:
              self.ignored_lines = ignored_lines
          else:
              self.ignored_lines = {}
  
      def local_definitions(self) -> Iterator[Definition]:
          """Return all definitions within the module (including nested).
  
          This doesn't include imported definitions.
          """
          return local_definitions(self.names, self.fullname)
  
      @property
      def name(self) -> str:
          return '' if not self._fullname else self._fullname.split('.')[-1]
  
      @property
      def fullname(self) -> Bogus[str]:
          return self._fullname
  
      def accept(self, visitor: NodeVisitor[T]) -> T:
          return visitor.visit_mypy_file(self)
  
      def is_package_init_file(self) -> bool:
          return len(self.path) != 0 and os.path.basename(self.path).startswith('__init__.')
  
      def serialize(self) -> JsonDict:
          return {'.class': 'MypyFile',
                  '_fullname': self._fullname,
                  'names': self.names.serialize(self._fullname),
                  'is_stub': self.is_stub,
                  'path': self.path,
                  'is_partial_stub_package': self.is_partial_stub_package,
                  }
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'MypyFile':
          assert data['.class'] == 'MypyFile', data
          tree = MypyFile([], [])
          tree._fullname = data['_fullname']
          tree.names = SymbolTable.deserialize(data['names'])
          tree.is_stub = data['is_stub']
          tree.path = data['path']
          tree.is_partial_stub_package = data['is_partial_stub_package']
          tree.is_cache_skeleton = True
          return tree
  
  
  class ImportBase(Statement):
      """Base class for all import statements."""
  
      is_unreachable = False  # Set by semanal.SemanticAnalyzerPass1 if inside `if False` etc.
      is_top_level = False  # Ditto if outside any class or def
      is_mypy_only = False  # Ditto if inside `if TYPE_CHECKING` or `if MYPY`
  
      # If an import replaces existing definitions, we construct dummy assignment
      # statements that assign the imported names to the names in the current scope,
      # for type checking purposes. Example:
      #
      #     x = 1
      #     from m import x   <-- add assignment representing "x = m.x"
      assignments = None  # type: List[AssignmentStmt]
  
      def __init__(self) -> None:
          super().__init__()
          self.assignments = []
  
  
  class Import(ImportBase):
      """import m [as n]"""
  
      ids = None  # type: List[Tuple[str, Optional[str]]]     # (module id, as id)
  
      def __init__(self, ids: List[Tuple[str, Optional[str]]]) -> None:
          super().__init__()
          self.ids = ids
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_import(self)
  
  
  class ImportFrom(ImportBase):
      """from m import x [as y], ..."""
  
      id = None  # type: str
      relative = None  # type: int
      names = None  # type: List[Tuple[str, Optional[str]]]  # Tuples (name, as name)
  
      def __init__(self, id: str, relative: int, names: List[Tuple[str, Optional[str]]]) -> None:
          super().__init__()
          self.id = id
          self.names = names
          self.relative = relative
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_import_from(self)
  
  
  class ImportAll(ImportBase):
      """from m import *"""
      id = None  # type: str
      relative = None  # type: int
      # NOTE: Only filled and used by old semantic analyzer.
      imported_names = None  # type: List[str]
  
      def __init__(self, id: str, relative: int) -> None:
          super().__init__()
          self.id = id
          self.relative = relative
          self.imported_names = []
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_import_all(self)
  
  
  class ImportedName(SymbolNode):
      """Indirect reference to a fullname stored in symbol table.
  
      This node is not present in the original program as such. This is
      just a temporary artifact in binding imported names. After semantic
      analysis pass 2, these references should be replaced with direct
      reference to a real AST node.
  
      Note that this is neither a Statement nor an Expression so this
      can't be visited.
      """
  
      def __init__(self, target_fullname: str) -> None:
          super().__init__()
          self.target_fullname = target_fullname
  
      @property
      def name(self) -> str:
          return self.target_fullname.split('.')[-1]
  
      @property
      def fullname(self) -> str:
          return self.target_fullname
  
      def serialize(self) -> JsonDict:
          assert False, "ImportedName leaked from semantic analysis"
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'ImportedName':
          assert False, "ImportedName should never be serialized"
  
      def __str__(self) -> str:
          return 'ImportedName(%s)' % self.target_fullname
  
  
  FUNCBASE_FLAGS = [
      'is_property', 'is_class', 'is_static', 'is_final'
  ]  # type: Final
  
  
  class FuncBase(Node):
      """Abstract base class for function-like nodes.
  
      N.B: Although this has SymbolNode subclasses (FuncDef,
      OverloadedFuncDef), avoid calling isinstance(..., FuncBase) on
      something that is typed as SymbolNode.  This is to work around
      mypy bug #3603, in which mypy doesn't understand multiple
      inheritance very well, and will assume that a SymbolNode
      cannot be a FuncBase.
  
      Instead, test against SYMBOL_FUNCBASE_TYPES, which enumerates
      SymbolNode subclasses that are also FuncBase subclasses.
      """
  
      __slots__ = ('type',
                   'unanalyzed_type',
                   'info',
                   'is_property',
                   'is_class',        # Uses "@classmethod" (explicit or implicit)
                   'is_static',       # Uses "@staticmethod"
                   'is_final',        # Uses "@final"
                   '_fullname',
                   )
  
      def __init__(self) -> None:
          super().__init__()
          # Type signature. This is usually CallableType or Overloaded, but it can be
          # something else for decorated functions.
          self.type = None  # type: Optional[mypy.types.ProperType]
          # Original, not semantically analyzed type (used for reprocessing)
          self.unanalyzed_type = None  # type: Optional[mypy.types.ProperType]
          # If method, reference to TypeInfo
          # TODO: Type should be Optional[TypeInfo]
          self.info = FUNC_NO_INFO
          self.is_property = False
          self.is_class = False
          self.is_static = False
          self.is_final = False
          # Name with module prefix
          # TODO: Type should be Optional[str]
          self._fullname = cast(Bogus[str], None)
  
      @property
      @abstractmethod
      def name(self) -> str: pass
  
      @property
      def fullname(self) -> Bogus[str]:
          return self._fullname
  
  
  OverloadPart = Union['FuncDef', 'Decorator']
  
  
  class OverloadedFuncDef(FuncBase, SymbolNode, Statement):
      """A logical node representing all the variants of a multi-declaration function.
  
      A multi-declaration function is often an @overload, but can also be a
      @property with a setter and a/or a deleter.
  
      This node has no explicit representation in the source program.
      Overloaded variants must be consecutive in the source file.
      """
  
      items = None  # type: List[OverloadPart]
      unanalyzed_items = None  # type: List[OverloadPart]
      impl = None  # type: Optional[OverloadPart]
  
      def __init__(self, items: List['OverloadPart']) -> None:
          super().__init__()
          self.items = items
          self.unanalyzed_items = items.copy()
          self.impl = None
          if len(items) > 0:
              self.set_line(items[0].line, items[0].column)
          self.is_final = False
  
      @property
      def name(self) -> str:
          if self.items:
              return self.items[0].name
          else:
              # This may happen for malformed overload
              assert self.impl is not None
              return self.impl.name
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_overloaded_func_def(self)
  
      def serialize(self) -> JsonDict:
          return {'.class': 'OverloadedFuncDef',
                  'items': [i.serialize() for i in self.items],
                  'type': None if self.type is None else self.type.serialize(),
                  'fullname': self._fullname,
                  'impl': None if self.impl is None else self.impl.serialize(),
                  'flags': get_flags(self, FUNCBASE_FLAGS),
                  }
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'OverloadedFuncDef':
          assert data['.class'] == 'OverloadedFuncDef'
          res = OverloadedFuncDef([
              cast(OverloadPart, SymbolNode.deserialize(d))
              for d in data['items']])
          if data.get('impl') is not None:
              res.impl = cast(OverloadPart, SymbolNode.deserialize(data['impl']))
              # set line for empty overload items, as not set in __init__
              if len(res.items) > 0:
                  res.set_line(res.impl.line)
          if data.get('type') is not None:
              typ = mypy.types.deserialize_type(data['type'])
              assert isinstance(typ, mypy.types.ProperType)
              res.type = typ
          res._fullname = data['fullname']
          set_flags(res, data['flags'])
          # NOTE: res.info will be set in the fixup phase.
          return res
  
  
  class Argument(Node):
      """A single argument in a FuncItem."""
  
      __slots__ = ('variable', 'type_annotation', 'initializer', 'kind')
  
      def __init__(self,
                   variable: 'Var',
                   type_annotation: 'Optional[mypy.types.Type]',
                   initializer: Optional[Expression],
                   kind: int) -> None:
          super().__init__()
          self.variable = variable
          self.type_annotation = type_annotation
          self.initializer = initializer
          self.kind = kind  # must be an ARG_* constant
  
      def set_line(self,
                   target: Union[Context, int],
                   column: Optional[int] = None,
                   end_line: Optional[int] = None) -> None:
          super().set_line(target, column, end_line)
  
          if self.initializer and self.initializer.line < 0:
              self.initializer.set_line(self.line, self.column, self.end_line)
  
          self.variable.set_line(self.line, self.column, self.end_line)
  
  
  FUNCITEM_FLAGS = FUNCBASE_FLAGS + [
      'is_overload', 'is_generator', 'is_coroutine', 'is_async_generator',
      'is_awaitable_coroutine',
  ]  # type: Final
  
  
  class FuncItem(FuncBase):
      """Base class for nodes usable as overloaded function items."""
  
      __slots__ = ('arguments',  # Note that can be None if deserialized (type is a lie!)
                   'arg_names',  # Names of arguments
                   'arg_kinds',  # Kinds of arguments
                   'min_args',  # Minimum number of arguments
                   'max_pos',  # Maximum number of positional arguments, -1 if no explicit
                               # limit (*args not included)
                   'body',  # Body of the function
                   'is_overload',  # Is this an overload variant of function with more than
                                   # one overload variant?
                   'is_generator',  # Contains a yield statement?
                   'is_coroutine',  # Defined using 'async def' syntax?
                   'is_async_generator',  # Is an async def generator?
                   'is_awaitable_coroutine',  # Decorated with '@{typing,asyncio}.coroutine'?
                   'expanded',  # Variants of function with type variables with values expanded
                   )
  
      def __init__(self,
                   arguments: List[Argument],
                   body: 'Block',
                   typ: 'Optional[mypy.types.FunctionLike]' = None) -> None:
          super().__init__()
          self.arguments = arguments
          self.arg_names = [arg.variable.name for arg in self.arguments]
          self.arg_kinds = [arg.kind for arg in self.arguments]  # type: List[int]
          self.max_pos = self.arg_kinds.count(ARG_POS) + self.arg_kinds.count(ARG_OPT)
          self.body = body
          self.type = typ
          self.unanalyzed_type = typ
          self.is_overload = False
          self.is_generator = False
          self.is_coroutine = False
          self.is_async_generator = False
          self.is_awaitable_coroutine = False
          self.expanded = []  # type: List[FuncItem]
  
          self.min_args = 0
          for i in range(len(self.arguments)):
              if self.arguments[i] is None and i < self.max_fixed_argc():
                  self.min_args = i + 1
  
      def max_fixed_argc(self) -> int:
          return self.max_pos
  
      def set_line(self,
                   target: Union[Context, int],
                   column: Optional[int] = None,
                   end_line: Optional[int] = None) -> None:
          super().set_line(target, column, end_line)
          for arg in self.arguments:
              arg.set_line(self.line, self.column, self.end_line)
  
      def is_dynamic(self) -> bool:
          return self.type is None
  
  
  FUNCDEF_FLAGS = FUNCITEM_FLAGS + [
      'is_decorated', 'is_conditional', 'is_abstract',
  ]  # type: Final
  
  
  class FuncDef(FuncItem, SymbolNode, Statement):
      """Function definition.
  
      This is a non-lambda function defined using 'def'.
      """
  
      __slots__ = ('_name',
                   'is_decorated',
                   'is_conditional',
                   'is_abstract',
                   'original_def',
                   )
  
      def __init__(self,
                   name: str,              # Function name
                   arguments: List[Argument],
                   body: 'Block',
                   typ: 'Optional[mypy.types.FunctionLike]' = None) -> None:
          super().__init__(arguments, body, typ)
          self._name = name
          self.is_decorated = False
          self.is_conditional = False  # Defined conditionally (within block)?
          self.is_abstract = False
          self.is_final = False
          # Original conditional definition
          self.original_def = None  # type: Union[None, FuncDef, Var, Decorator]
  
      @property
      def name(self) -> str:
          return self._name
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_func_def(self)
  
      def serialize(self) -> JsonDict:
          # We're deliberating omitting arguments and storing only arg_names and
          # arg_kinds for space-saving reasons (arguments is not used in later
          # stages of mypy).
          # TODO: After a FuncDef is deserialized, the only time we use `arg_names`
          # and `arg_kinds` is when `type` is None and we need to infer a type. Can
          # we store the inferred type ahead of time?
          return {'.class': 'FuncDef',
                  'name': self._name,
                  'fullname': self._fullname,
                  'arg_names': self.arg_names,
                  'arg_kinds': self.arg_kinds,
                  'type': None if self.type is None else self.type.serialize(),
                  'flags': get_flags(self, FUNCDEF_FLAGS),
                  # TODO: Do we need expanded, original_def?
                  }
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'FuncDef':
          assert data['.class'] == 'FuncDef'
          body = Block([])
          ret = FuncDef(data['name'],
                        [],
                        body,
                        (None if data['type'] is None
                         else cast(mypy.types.FunctionLike,
                                   mypy.types.deserialize_type(data['type']))))
          ret._fullname = data['fullname']
          set_flags(ret, data['flags'])
          # NOTE: ret.info is set in the fixup phase.
          ret.arg_names = data['arg_names']
          ret.arg_kinds = data['arg_kinds']
          # Leave these uninitialized so that future uses will trigger an error
          del ret.arguments
          del ret.max_pos
          del ret.min_args
          return ret
  
  
  # All types that are both SymbolNodes and FuncBases. See the FuncBase
  # docstring for the rationale.
  SYMBOL_FUNCBASE_TYPES = (OverloadedFuncDef, FuncDef)
  
  
  class Decorator(SymbolNode, Statement):
      """A decorated function.
  
      A single Decorator object can include any number of function decorators.
      """
  
      func = None  # type: FuncDef                # Decorated function
      decorators = None  # type: List[Expression] # Decorators (may be empty)
      # Some decorators are removed by semanal, keep the original here.
      original_decorators = None  # type: List[Expression]
      # TODO: This is mostly used for the type; consider replacing with a 'type' attribute
      var = None  # type: Var                     # Represents the decorated function obj
      is_overload = False
  
      def __init__(self, func: FuncDef, decorators: List[Expression],
                   var: 'Var') -> None:
          super().__init__()
          self.func = func
          self.decorators = decorators
          self.original_decorators = decorators.copy()
          self.var = var
          self.is_overload = False
  
      @property
      def name(self) -> str:
          return self.func.name
  
      @property
      def fullname(self) -> Bogus[str]:
          return self.func.fullname
  
      @property
      def is_final(self) -> bool:
          return self.func.is_final
  
      @property
      def info(self) -> 'TypeInfo':
          return self.func.info
  
      @property
      def type(self) -> 'Optional[mypy.types.Type]':
          return self.var.type
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_decorator(self)
  
      def serialize(self) -> JsonDict:
          return {'.class': 'Decorator',
                  'func': self.func.serialize(),
                  'var': self.var.serialize(),
                  'is_overload': self.is_overload,
                  }
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'Decorator':
          assert data['.class'] == 'Decorator'
          dec = Decorator(FuncDef.deserialize(data['func']),
                          [],
                          Var.deserialize(data['var']))
          dec.is_overload = data['is_overload']
          return dec
  
  
  VAR_FLAGS = [
      'is_self', 'is_initialized_in_class', 'is_staticmethod',
      'is_classmethod', 'is_property', 'is_settable_property', 'is_suppressed_import',
      'is_classvar', 'is_abstract_var', 'is_final', 'final_unset_in_class', 'final_set_in_init',
      'explicit_self_type', 'is_ready',
  ]  # type: Final
  
  
  class Var(SymbolNode):
      """A variable.
  
      It can refer to global/local variable or a data attribute.
      """
  
      __slots__ = ('_name',
                   '_fullname',
                   'info',
                   'type',
                   'final_value',
                   'is_self',
                   'is_ready',
                   'is_inferred',
                   'is_initialized_in_class',
                   'is_staticmethod',
                   'is_classmethod',
                   'is_property',
                   'is_settable_property',
                   'is_classvar',
                   'is_abstract_var',
                   'is_final',
                   'final_unset_in_class',
                   'final_set_in_init',
                   'is_suppressed_import',
                   'explicit_self_type',
                   'from_module_getattr',
                   )
  
      def __init__(self, name: str, type: 'Optional[mypy.types.Type]' = None) -> None:
          super().__init__()
          self._name = name   # Name without module prefix
          # TODO: Should be Optional[str]
          self._fullname = cast('Bogus[str]', None)  # Name with module prefix
          # TODO: Should be Optional[TypeInfo]
          self.info = VAR_NO_INFO
          self.type = type  # type: Optional[mypy.types.Type] # Declared or inferred type, or None
          # Is this the first argument to an ordinary method (usually "self")?
          self.is_self = False
          self.is_ready = True  # If inferred, is the inferred type available?
          self.is_inferred = (self.type is None)
          # Is this initialized explicitly to a non-None value in class body?
          self.is_initialized_in_class = False
          self.is_staticmethod = False
          self.is_classmethod = False
          self.is_property = False
          self.is_settable_property = False
          self.is_classvar = False
          self.is_abstract_var = False
          # Set to true when this variable refers to a module we were unable to
          # parse for some reason (eg a silenced module)
          self.is_suppressed_import = False
          # Was this "variable" (rather a constant) defined as Final[...]?
          self.is_final = False
          # If constant value is a simple literal,
          # store the literal value (unboxed) for the benefit of
          # tools like mypyc.
          self.final_value = None  # type: Optional[Union[int, float, bool, str]]
          # Where the value was set (only for class attributes)
          self.final_unset_in_class = False
          self.final_set_in_init = False
          # This is True for a variable that was declared on self with an explicit type:
          #     class C:
          #         def __init__(self) -> None:
          #             self.x: int
          # This case is important because this defines a new Var, even if there is one
          # present in a superclass (without explicit type this doesn't create a new Var).
          # See SemanticAnalyzer.analyze_member_lvalue() for details.
          self.explicit_self_type = False
          # If True, this is an implicit Var created due to module-level __getattr__.
          self.from_module_getattr = False
  
      @property
      def name(self) -> str:
          return self._name
  
      @property
      def fullname(self) -> Bogus[str]:
          return self._fullname
  
      def accept(self, visitor: NodeVisitor[T]) -> T:
          return visitor.visit_var(self)
  
      def serialize(self) -> JsonDict:
          # TODO: Leave default values out?
          # NOTE: Sometimes self.is_ready is False here, but we don't care.
          data = {'.class': 'Var',
                  'name': self._name,
                  'fullname': self._fullname,
                  'type': None if self.type is None else self.type.serialize(),
                  'flags': get_flags(self, VAR_FLAGS),
                  }  # type: JsonDict
          if self.final_value is not None:
              data['final_value'] = self.final_value
          return data
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'Var':
          assert data['.class'] == 'Var'
          name = data['name']
          type = None if data['type'] is None else mypy.types.deserialize_type(data['type'])
          v = Var(name, type)
          v.is_ready = False  # Override True default set in __init__
          v._fullname = data['fullname']
          set_flags(v, data['flags'])
          v.final_value = data.get('final_value')
          return v
  
  
  class ClassDef(Statement):
      """Class definition"""
  
      name = None  # type: str       # Name of the class without module prefix
      fullname = None  # type: Bogus[str]   # Fully qualified name of the class
      defs = None  # type: Block
      type_vars = None  # type: List[mypy.types.TypeVarDef]
      # Base class expressions (not semantically analyzed -- can be arbitrary expressions)
      base_type_exprs = None  # type: List[Expression]
      # Special base classes like Generic[...] get moved here during semantic analysis
      removed_base_type_exprs = None  # type: List[Expression]
      info = None  # type: TypeInfo  # Related TypeInfo
      metaclass = None  # type: Optional[Expression]
      decorators = None  # type: List[Expression]
      keywords = None  # type: OrderedDict[str, Expression]
      analyzed = None  # type: Optional[Expression]
      has_incompatible_baseclass = False
  
      def __init__(self,
                   name: str,
                   defs: 'Block',
                   type_vars: Optional[List['mypy.types.TypeVarDef']] = None,
                   base_type_exprs: Optional[List[Expression]] = None,
                   metaclass: Optional[Expression] = None,
                   keywords: Optional[List[Tuple[str, Expression]]] = None) -> None:
          super().__init__()
          self.name = name
          self.defs = defs
          self.type_vars = type_vars or []
          self.base_type_exprs = base_type_exprs or []
          self.removed_base_type_exprs = []
          self.info = CLASSDEF_NO_INFO
          self.metaclass = metaclass
          self.decorators = []
          self.keywords = OrderedDict(keywords or [])
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_class_def(self)
  
      def is_generic(self) -> bool:
          return self.info.is_generic()
  
      def serialize(self) -> JsonDict:
          # Not serialized: defs, base_type_exprs, metaclass, decorators,
          # analyzed (for named tuples etc.)
          return {'.class': 'ClassDef',
                  'name': self.name,
                  'fullname': self.fullname,
                  'type_vars': [v.serialize() for v in self.type_vars],
                  }
  
      @classmethod
      def deserialize(self, data: JsonDict) -> 'ClassDef':
          assert data['.class'] == 'ClassDef'
          res = ClassDef(data['name'],
                         Block([]),
                         [mypy.types.TypeVarDef.deserialize(v) for v in data['type_vars']],
                         )
          res.fullname = data['fullname']
          return res
  
  
  class GlobalDecl(Statement):
      """Declaration global x, y, ..."""
  
      names = None  # type: List[str]
  
      def __init__(self, names: List[str]) -> None:
          super().__init__()
          self.names = names
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_global_decl(self)
  
  
  class NonlocalDecl(Statement):
      """Declaration nonlocal x, y, ..."""
  
      names = None  # type: List[str]
  
      def __init__(self, names: List[str]) -> None:
          super().__init__()
          self.names = names
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_nonlocal_decl(self)
  
  
  class Block(Statement):
      __slots__ = ('body', 'is_unreachable')
  
      def __init__(self, body: List[Statement]) -> None:
          super().__init__()
          self.body = body
          # True if we can determine that this block is not executed during semantic
          # analysis. For example, this applies to blocks that are protected by
          # something like "if PY3:" when using Python 2. However, some code is
          # only considered unreachable during type checking and this is not true
          # in those cases.
          self.is_unreachable = False
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_block(self)
  
  
  # Statements
  
  
  class ExpressionStmt(Statement):
      """An expression as a statement, such as print(s)."""
      expr = None  # type: Expression
  
      def __init__(self, expr: Expression) -> None:
          super().__init__()
          self.expr = expr
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_expression_stmt(self)
  
  
  class AssignmentStmt(Statement):
      """Assignment statement.
  
      The same node class is used for single assignment, multiple assignment
      (e.g. x, y = z) and chained assignment (e.g. x = y = z), assignments
      that define new names, and assignments with explicit types ("# type: t"
      or "x: t [= ...]").
  
      An lvalue can be NameExpr, TupleExpr, ListExpr, MemberExpr, or IndexExpr.
      """
  
      lvalues = None  # type: List[Lvalue]
      # This is a TempNode if and only if no rvalue (x: t).
      rvalue = None  # type: Expression
      # Declared type in a comment, may be None.
      type = None  # type: Optional[mypy.types.Type]
      # Original, not semantically analyzed type in annotation (used for reprocessing)
      unanalyzed_type = None  # type: Optional[mypy.types.Type]
      # This indicates usage of PEP 526 type annotation syntax in assignment.
      new_syntax = False  # type: bool
      # Does this assignment define a type alias?
      is_alias_def = False
      # Is this a final definition?
      # Final attributes can't be re-assigned once set, and can't be overridden
      # in a subclass. This flag is not set if an attempted declaration was found to
      # be invalid during semantic analysis. It is still set to `True` if
      # a final declaration overrides another final declaration (this is checked
      # during type checking when MROs are known).
      is_final_def = False
  
      def __init__(self, lvalues: List[Lvalue], rvalue: Expression,
                   type: 'Optional[mypy.types.Type]' = None, new_syntax: bool = False) -> None:
          super().__init__()
          self.lvalues = lvalues
          self.rvalue = rvalue
          self.type = type
          self.unanalyzed_type = type
          self.new_syntax = new_syntax
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_assignment_stmt(self)
  
  
  class OperatorAssignmentStmt(Statement):
      """Operator assignment statement such as x += 1"""
  
      op = ''
      lvalue = None  # type: Lvalue
      rvalue = None  # type: Expression
  
      def __init__(self, op: str, lvalue: Lvalue, rvalue: Expression) -> None:
          super().__init__()
          self.op = op
          self.lvalue = lvalue
          self.rvalue = rvalue
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_operator_assignment_stmt(self)
  
  
  class WhileStmt(Statement):
      expr = None  # type: Expression
      body = None  # type: Block
      else_body = None  # type: Optional[Block]
  
      def __init__(self, expr: Expression, body: Block, else_body: Optional[Block]) -> None:
          super().__init__()
          self.expr = expr
          self.body = body
          self.else_body = else_body
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_while_stmt(self)
  
  
  class ForStmt(Statement):
      # Index variables
      index = None  # type: Lvalue
      # Type given by type comments for index, can be None
      index_type = None  # type: Optional[mypy.types.Type]
      # Original, not semantically analyzed type in annotation (used for reprocessing)
      unanalyzed_index_type = None  # type: Optional[mypy.types.Type]
      # Inferred iterable item type
      inferred_item_type = None  # type: Optional[mypy.types.Type]
      # Inferred iterator type
      inferred_iterator_type = None  # type: Optional[mypy.types.Type]
      # Expression to iterate
      expr = None  # type: Expression
      body = None  # type: Block
      else_body = None  # type: Optional[Block]
      is_async = False  # True if `async for ...` (PEP 492, Python 3.5)
  
      def __init__(self,
                   index: Lvalue,
                   expr: Expression,
                   body: Block,
                   else_body: Optional[Block],
                   index_type: 'Optional[mypy.types.Type]' = None) -> None:
          super().__init__()
          self.index = index
          self.index_type = index_type
          self.unanalyzed_index_type = index_type
          self.expr = expr
          self.body = body
          self.else_body = else_body
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_for_stmt(self)
  
  
  class ReturnStmt(Statement):
      expr = None  # type: Optional[Expression]
  
      def __init__(self, expr: Optional[Expression]) -> None:
          super().__init__()
          self.expr = expr
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_return_stmt(self)
  
  
  class AssertStmt(Statement):
      expr = None  # type: Expression
      msg = None  # type: Optional[Expression]
  
      def __init__(self, expr: Expression, msg: Optional[Expression] = None) -> None:
          super().__init__()
          self.expr = expr
          self.msg = msg
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_assert_stmt(self)
  
  
  class DelStmt(Statement):
      expr = None  # type: Lvalue
  
      def __init__(self, expr: Lvalue) -> None:
          super().__init__()
          self.expr = expr
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_del_stmt(self)
  
  
  class BreakStmt(Statement):
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_break_stmt(self)
  
  
  class ContinueStmt(Statement):
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_continue_stmt(self)
  
  
  class PassStmt(Statement):
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_pass_stmt(self)
  
  
  class IfStmt(Statement):
      expr = None  # type: List[Expression]
      body = None  # type: List[Block]
      else_body = None  # type: Optional[Block]
  
      def __init__(self, expr: List[Expression], body: List[Block],
                   else_body: Optional[Block]) -> None:
          super().__init__()
          self.expr = expr
          self.body = body
          self.else_body = else_body
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_if_stmt(self)
  
  
  class RaiseStmt(Statement):
      # Plain 'raise' is a valid statement.
      expr = None  # type: Optional[Expression]
      from_expr = None  # type: Optional[Expression]
  
      def __init__(self, expr: Optional[Expression], from_expr: Optional[Expression]) -> None:
          super().__init__()
          self.expr = expr
          self.from_expr = from_expr
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_raise_stmt(self)
  
  
  class TryStmt(Statement):
      body = None  # type: Block                # Try body
      # Plain 'except:' also possible
      types = None  # type: List[Optional[Expression]]    # Except type expressions
      vars = None  # type: List[Optional[NameExpr]]     # Except variable names
      handlers = None  # type: List[Block]      # Except bodies
      else_body = None  # type: Optional[Block]
      finally_body = None  # type: Optional[Block]
  
      def __init__(self, body: Block, vars: List['Optional[NameExpr]'],
                   types: List[Optional[Expression]],
                   handlers: List[Block], else_body: Optional[Block],
                   finally_body: Optional[Block]) -> None:
          super().__init__()
          self.body = body
          self.vars = vars
          self.types = types
          self.handlers = handlers
          self.else_body = else_body
          self.finally_body = finally_body
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_try_stmt(self)
  
  
  class WithStmt(Statement):
      expr = None  # type: List[Expression]
      target = None  # type: List[Optional[Lvalue]]
      # Type given by type comments for target, can be None
      unanalyzed_type = None  # type: Optional[mypy.types.Type]
      # Semantically analyzed types from type comment (TypeList type expanded)
      analyzed_types = None  # type: List[mypy.types.Type]
      body = None  # type: Block
      is_async = False  # True if `async with ...` (PEP 492, Python 3.5)
  
      def __init__(self, expr: List[Expression], target: List[Optional[Lvalue]],
                   body: Block, target_type: 'Optional[mypy.types.Type]' = None) -> None:
          super().__init__()
          self.expr = expr
          self.target = target
          self.unanalyzed_type = target_type
          self.analyzed_types = []
          self.body = body
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_with_stmt(self)
  
  
  class PrintStmt(Statement):
      """Python 2 print statement"""
  
      args = None  # type: List[Expression]
      newline = False
      # The file-like target object (given using >>).
      target = None  # type: Optional[Expression]
  
      def __init__(self,
                   args: List[Expression],
                   newline: bool,
                   target: Optional[Expression] = None) -> None:
          super().__init__()
          self.args = args
          self.newline = newline
          self.target = target
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_print_stmt(self)
  
  
  class ExecStmt(Statement):
      """Python 2 exec statement"""
  
      expr = None  # type: Expression
      globals = None  # type: Optional[Expression]
      locals = None  # type: Optional[Expression]
  
      def __init__(self, expr: Expression,
                   globals: Optional[Expression],
                   locals: Optional[Expression]) -> None:
          super().__init__()
          self.expr = expr
          self.globals = globals
          self.locals = locals
  
      def accept(self, visitor: StatementVisitor[T]) -> T:
          return visitor.visit_exec_stmt(self)
  
  
  # Expressions
  
  
  class IntExpr(Expression):
      """Integer literal"""
  
      value = 0
  
      def __init__(self, value: int) -> None:
          super().__init__()
          self.value = value
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_int_expr(self)
  
  
  # How mypy uses StrExpr, BytesExpr, and UnicodeExpr:
  # In Python 2 mode:
  # b'x', 'x' -> StrExpr
  # u'x' -> UnicodeExpr
  # BytesExpr is unused
  #
  # In Python 3 mode:
  # b'x' -> BytesExpr
  # 'x', u'x' -> StrExpr
  # UnicodeExpr is unused
  
  class StrExpr(Expression):
      """String literal"""
  
      value = ''
  
      # Keeps track of whether this string originated from Python 2 source code vs
      # Python 3 source code. We need to keep track of this information so we can
      # correctly handle types that have "nested strings". For example, consider this
      # type alias, where we have a forward reference to a literal type:
      #
      #     Alias = List["Literal['foo']"]
      #
      # When parsing this, we need to know whether the outer string and alias came from
      # Python 2 code vs Python 3 code so we can determine whether the inner `Literal['foo']`
      # is meant to be `Literal[u'foo']` or `Literal[b'foo']`.
      #
      # This field keeps track of that information.
      from_python_3 = True
  
      def __init__(self, value: str, from_python_3: bool = False) -> None:
          super().__init__()
          self.value = value
          self.from_python_3 = from_python_3
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_str_expr(self)
  
  
  class BytesExpr(Expression):
      """Bytes literal"""
  
      # Note: we deliberately do NOT use bytes here because it ends up
      # unnecessarily complicating a lot of the result logic. For example,
      # we'd have to worry about converting the bytes into a format we can
      # easily serialize/deserialize to and from JSON, would have to worry
      # about turning the bytes into a human-readable representation in
      # error messages...
      #
      # It's more convenient to just store the human-readable representation
      # from the very start.
      value = ''
  
      def __init__(self, value: str) -> None:
          super().__init__()
          self.value = value
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_bytes_expr(self)
  
  
  class UnicodeExpr(Expression):
      """Unicode literal (Python 2.x)"""
  
      value = ''
  
      def __init__(self, value: str) -> None:
          super().__init__()
          self.value = value
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_unicode_expr(self)
  
  
  class FloatExpr(Expression):
      """Float literal"""
  
      value = 0.0
  
      def __init__(self, value: float) -> None:
          super().__init__()
          self.value = value
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_float_expr(self)
  
  
  class ComplexExpr(Expression):
      """Complex literal"""
  
      def __init__(self, value: complex) -> None:
          super().__init__()
          self.value = value
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_complex_expr(self)
  
  
  class EllipsisExpr(Expression):
      """Ellipsis (...)"""
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_ellipsis(self)
  
  
  class StarExpr(Expression):
      """Star expression"""
  
      expr = None  # type: Expression
  
      def __init__(self, expr: Expression) -> None:
          super().__init__()
          self.expr = expr
  
          # Whether this starred expression is used in a tuple/list and as lvalue
          self.valid = False
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_star_expr(self)
  
  
  class RefExpr(Expression):
      """Abstract base class for name-like constructs"""
  
      __slots__ = ('kind', 'node', 'fullname', 'is_new_def', 'is_inferred_def', 'is_alias_rvalue')
  
      def __init__(self) -> None:
          super().__init__()
          # LDEF/GDEF/MDEF/... (None if not available)
          self.kind = None  # type: Optional[int]
          # Var, FuncDef or TypeInfo that describes this
          self.node = None  # type: Optional[SymbolNode]
          # Fully qualified name (or name if not global)
          self.fullname = None  # type: Optional[str]
          # Does this define a new name?
          self.is_new_def = False
          # Does this define a new name with inferred type?
          #
          # For members, after semantic analysis, this does not take base
          # classes into consideration at all; the type checker deals with these.
          self.is_inferred_def = False
          # Is this expression appears as an rvalue of a valid type alias definition?
          self.is_alias_rvalue = False
  
  
  class NameExpr(RefExpr):
      """Name expression
  
      This refers to a local name, global name or a module.
      """
  
      __slots__ = ('name', 'is_special_form')
  
      def __init__(self, name: str) -> None:
          super().__init__()
          self.name = name  # Name referred to (may be qualified)
          # Is this a l.h.s. of a special form assignment like typed dict or type variable?
          self.is_special_form = False
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_name_expr(self)
  
      def serialize(self) -> JsonDict:
          assert False, "Serializing NameExpr: %s" % (self,)
  
  
  class MemberExpr(RefExpr):
      """Member access expression x.y"""
  
      __slots__ = ('expr', 'name', 'def_var')
  
      def __init__(self, expr: Expression, name: str) -> None:
          super().__init__()
          self.expr = expr
          self.name = name
          # The variable node related to a definition through 'self.x = <initializer>'.
          # The nodes of other kinds of member expressions are resolved during type checking.
          self.def_var = None  # type: Optional[Var]
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_member_expr(self)
  
  
  # Kinds of arguments
  
  # Positional argument
  ARG_POS = 0  # type: Final[int]
  # Positional, optional argument (functions only, not calls)
  ARG_OPT = 1  # type: Final[int]
  # *arg argument
  ARG_STAR = 2  # type: Final[int]
  # Keyword argument x=y in call, or keyword-only function arg
  ARG_NAMED = 3  # type: Final[int]
  # **arg argument
  ARG_STAR2 = 4  # type: Final[int]
  # In an argument list, keyword-only and also optional
  ARG_NAMED_OPT = 5  # type: Final[int]
  
  
  class CallExpr(Expression):
      """Call expression.
  
      This can also represent several special forms that are syntactically calls
      such as cast(...) and None  # type: ....
      """
  
      __slots__ = ('callee', 'args', 'arg_kinds', 'arg_names', 'analyzed')
  
      def __init__(self,
                   callee: Expression,
                   args: List[Expression],
                   arg_kinds: List[int],
                   arg_names: List[Optional[str]],
                   analyzed: Optional[Expression] = None) -> None:
          super().__init__()
          if not arg_names:
              arg_names = [None] * len(args)
  
          self.callee = callee
          self.args = args
          self.arg_kinds = arg_kinds  # ARG_ constants
          # Each name can be None if not a keyword argument.
          self.arg_names = arg_names  # type: List[Optional[str]]
          # If not None, the node that represents the meaning of the CallExpr. For
          # cast(...) this is a CastExpr.
          self.analyzed = analyzed
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_call_expr(self)
  
  
  class YieldFromExpr(Expression):
      expr = None  # type: Expression
  
      def __init__(self, expr: Expression) -> None:
          super().__init__()
          self.expr = expr
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_yield_from_expr(self)
  
  
  class YieldExpr(Expression):
      expr = None  # type: Optional[Expression]
  
      def __init__(self, expr: Optional[Expression]) -> None:
          super().__init__()
          self.expr = expr
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_yield_expr(self)
  
  
  class IndexExpr(Expression):
      """Index expression x[y].
  
      Also wraps type application such as List[int] as a special form.
      """
  
      base = None  # type: Expression
      index = None  # type: Expression
      # Inferred __getitem__ method type
      method_type = None  # type: Optional[mypy.types.Type]
      # If not None, this is actually semantically a type application
      # Class[type, ...] or a type alias initializer.
      analyzed = None  # type: Union[TypeApplication, TypeAliasExpr, None]
  
      def __init__(self, base: Expression, index: Expression) -> None:
          super().__init__()
          self.base = base
          self.index = index
          self.analyzed = None
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_index_expr(self)
  
  
  class UnaryExpr(Expression):
      """Unary operation"""
  
      op = ''
      expr = None  # type: Expression
      # Inferred operator method type
      method_type = None  # type: Optional[mypy.types.Type]
  
      def __init__(self, op: str, expr: Expression) -> None:
          super().__init__()
          self.op = op
          self.expr = expr
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_unary_expr(self)
  
  
  class AssignmentExpr(Expression):
      """Assignment expressions in Python 3.8+, like "a := 2"."""
      def __init__(self, target: Expression, value: Expression) -> None:
          super().__init__()
          self.target = target
          self.value = value
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_assignment_expr(self)
  
  
  # Map from binary operator id to related method name (in Python 3).
  op_methods = {
      '+': '__add__',
      '-': '__sub__',
      '*': '__mul__',
      '/': '__truediv__',
      '%': '__mod__',
      'divmod': '__divmod__',
      '//': '__floordiv__',
      '**': '__pow__',
      '@': '__matmul__',
      '&': '__and__',
      '|': '__or__',
      '^': '__xor__',
      '<<': '__lshift__',
      '>>': '__rshift__',
      '==': '__eq__',
      '!=': '__ne__',
      '<': '__lt__',
      '>=': '__ge__',
      '>': '__gt__',
      '<=': '__le__',
      'in': '__contains__',
  }  # type: Final[Dict[str, str]]
  
  op_methods_to_symbols = {v: k for (k, v) in op_methods.items()}  # type: Final
  op_methods_to_symbols['__div__'] = '/'
  
  comparison_fallback_method = '__cmp__'  # type: Final
  ops_falling_back_to_cmp = {'__ne__', '__eq__',
                             '__lt__', '__le__',
                             '__gt__', '__ge__'}  # type: Final
  
  
  ops_with_inplace_method = {
      '+', '-', '*', '/', '%', '//', '**', '@', '&', '|', '^', '<<', '>>'}  # type: Final
  
  inplace_operator_methods = set(
      '__i' + op_methods[op][2:] for op in ops_with_inplace_method)  # type: Final
  
  reverse_op_methods = {
      '__add__': '__radd__',
      '__sub__': '__rsub__',
      '__mul__': '__rmul__',
      '__truediv__': '__rtruediv__',
      '__mod__': '__rmod__',
      '__divmod__': '__rdivmod__',
      '__floordiv__': '__rfloordiv__',
      '__pow__': '__rpow__',
      '__matmul__': '__rmatmul__',
      '__and__': '__rand__',
      '__or__': '__ror__',
      '__xor__': '__rxor__',
      '__lshift__': '__rlshift__',
      '__rshift__': '__rrshift__',
      '__eq__': '__eq__',
      '__ne__': '__ne__',
      '__lt__': '__gt__',
      '__ge__': '__le__',
      '__gt__': '__lt__',
      '__le__': '__ge__',
  }  # type: Final
  
  # Suppose we have some class A. When we do A() + A(), Python will only check
  # the output of A().__add__(A()) and skip calling the __radd__ method entirely.
  # This shortcut is used only for the following methods:
  op_methods_that_shortcut = {
      '__add__',
      '__sub__',
      '__mul__',
      '__div__',
      '__truediv__',
      '__mod__',
      '__divmod__',
      '__floordiv__',
      '__pow__',
      '__matmul__',
      '__and__',
      '__or__',
      '__xor__',
      '__lshift__',
      '__rshift__',
  }  # type: Final
  
  normal_from_reverse_op = dict((m, n) for n, m in reverse_op_methods.items())  # type: Final
  reverse_op_method_set = set(reverse_op_methods.values())  # type: Final
  
  unary_op_methods = {
      '-': '__neg__',
      '+': '__pos__',
      '~': '__invert__',
  }  # type: Final
  
  
  class OpExpr(Expression):
      """Binary operation (other than . or [] or comparison operators,
      which have specific nodes)."""
  
      op = ''
      left = None  # type: Expression
      right = None  # type: Expression
      # Inferred type for the operator method type (when relevant).
      method_type = None  # type: Optional[mypy.types.Type]
      # Is the right side going to be evaluated every time?
      right_always = False
      # Is the right side unreachable?
      right_unreachable = False
  
      def __init__(self, op: str, left: Expression, right: Expression) -> None:
          super().__init__()
          self.op = op
          self.left = left
          self.right = right
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_op_expr(self)
  
  
  class ComparisonExpr(Expression):
      """Comparison expression (e.g. a < b > c < d)."""
  
      operators = None  # type: List[str]
      operands = None  # type: List[Expression]
      # Inferred type for the operator methods (when relevant; None for 'is').
      method_types = None  # type: List[Optional[mypy.types.Type]]
  
      def __init__(self, operators: List[str], operands: List[Expression]) -> None:
          super().__init__()
          self.operators = operators
          self.operands = operands
          self.method_types = []
  
      def pairwise(self) -> Iterator[Tuple[str, Expression, Expression]]:
          """If this comparison expr is "a < b is c == d", yields the sequence
          ("<", a, b), ("is", b, c), ("==", c, d)
          """
          for i, operator in enumerate(self.operators):
              yield operator, self.operands[i], self.operands[i + 1]
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_comparison_expr(self)
  
  
  class SliceExpr(Expression):
      """Slice expression (e.g. 'x:y', 'x:', '::2' or ':').
  
      This is only valid as index in index expressions.
      """
  
      begin_index = None  # type: Optional[Expression]
      end_index = None  # type: Optional[Expression]
      stride = None  # type: Optional[Expression]
  
      def __init__(self, begin_index: Optional[Expression],
                   end_index: Optional[Expression],
                   stride: Optional[Expression]) -> None:
          super().__init__()
          self.begin_index = begin_index
          self.end_index = end_index
          self.stride = stride
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_slice_expr(self)
  
  
  class CastExpr(Expression):
      """Cast expression cast(type, expr)."""
  
      expr = None  # type: Expression
      type = None  # type: mypy.types.Type
  
      def __init__(self, expr: Expression, typ: 'mypy.types.Type') -> None:
          super().__init__()
          self.expr = expr
          self.type = typ
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_cast_expr(self)
  
  
  class RevealExpr(Expression):
      """Reveal type expression reveal_type(expr) or reveal_locals() expression."""
  
      expr = None  # type: Optional[Expression]
      kind = 0  # type: int
      local_nodes = None  # type: Optional[List[Var]]
  
      def __init__(
              self, kind: int,
              expr: Optional[Expression] = None,
              local_nodes: 'Optional[List[Var]]' = None) -> None:
          super().__init__()
          self.expr = expr
          self.kind = kind
          self.local_nodes = local_nodes
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_reveal_expr(self)
  
  
  class SuperExpr(Expression):
      """Expression super().name"""
  
      name = ''
      info = None  # type: Optional[TypeInfo]  # Type that contains this super expression
      call = None  # type: CallExpr  # The expression super(...)
  
      def __init__(self, name: str, call: CallExpr) -> None:
          super().__init__()
          self.name = name
          self.call = call
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_super_expr(self)
  
  
  class LambdaExpr(FuncItem, Expression):
      """Lambda expression"""
  
      @property
      def name(self) -> str:
          return '<lambda>'
  
      def expr(self) -> Expression:
          """Return the expression (the body) of the lambda."""
          ret = cast(ReturnStmt, self.body.body[-1])
          expr = ret.expr
          assert expr is not None  # lambda can't have empty body
          return expr
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_lambda_expr(self)
  
      def is_dynamic(self) -> bool:
          return False
  
  
  class ListExpr(Expression):
      """List literal expression [...]."""
  
      items = None  # type: List[Expression]
  
      def __init__(self, items: List[Expression]) -> None:
          super().__init__()
          self.items = items
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_list_expr(self)
  
  
  class DictExpr(Expression):
      """Dictionary literal expression {key: value, ...}."""
  
      items = None  # type: List[Tuple[Optional[Expression], Expression]]
  
      def __init__(self, items: List[Tuple[Optional[Expression], Expression]]) -> None:
          super().__init__()
          self.items = items
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_dict_expr(self)
  
  
  class TupleExpr(Expression):
      """Tuple literal expression (..., ...)
  
      Also lvalue sequences (..., ...) and [..., ...]"""
  
      items = None  # type: List[Expression]
  
      def __init__(self, items: List[Expression]) -> None:
          super().__init__()
          self.items = items
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_tuple_expr(self)
  
  
  class SetExpr(Expression):
      """Set literal expression {value, ...}."""
  
      items = None  # type: List[Expression]
  
      def __init__(self, items: List[Expression]) -> None:
          super().__init__()
          self.items = items
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_set_expr(self)
  
  
  class GeneratorExpr(Expression):
      """Generator expression ... for ... in ... [ for ...  in ... ] [ if ... ]."""
  
      left_expr = None  # type: Expression
      sequences = None  # type: List[Expression]
      condlists = None  # type: List[List[Expression]]
      is_async = None  # type: List[bool]
      indices = None  # type: List[Lvalue]
  
      def __init__(self, left_expr: Expression, indices: List[Lvalue],
                   sequences: List[Expression], condlists: List[List[Expression]],
                   is_async: List[bool]) -> None:
          super().__init__()
          self.left_expr = left_expr
          self.sequences = sequences
          self.condlists = condlists
          self.indices = indices
          self.is_async = is_async
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_generator_expr(self)
  
  
  class ListComprehension(Expression):
      """List comprehension (e.g. [x + 1 for x in a])"""
  
      generator = None  # type: GeneratorExpr
  
      def __init__(self, generator: GeneratorExpr) -> None:
          super().__init__()
          self.generator = generator
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_list_comprehension(self)
  
  
  class SetComprehension(Expression):
      """Set comprehension (e.g. {x + 1 for x in a})"""
  
      generator = None  # type: GeneratorExpr
  
      def __init__(self, generator: GeneratorExpr) -> None:
          super().__init__()
          self.generator = generator
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_set_comprehension(self)
  
  
  class DictionaryComprehension(Expression):
      """Dictionary comprehension (e.g. {k: v for k, v in a}"""
  
      key = None  # type: Expression
      value = None  # type: Expression
      sequences = None  # type: List[Expression]
      condlists = None  # type: List[List[Expression]]
      is_async = None  # type: List[bool]
      indices = None  # type: List[Lvalue]
  
      def __init__(self, key: Expression, value: Expression, indices: List[Lvalue],
                   sequences: List[Expression], condlists: List[List[Expression]],
                   is_async: List[bool]) -> None:
          super().__init__()
          self.key = key
          self.value = value
          self.sequences = sequences
          self.condlists = condlists
          self.indices = indices
          self.is_async = is_async
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_dictionary_comprehension(self)
  
  
  class ConditionalExpr(Expression):
      """Conditional expression (e.g. x if y else z)"""
  
      cond = None  # type: Expression
      if_expr = None  # type: Expression
      else_expr = None  # type: Expression
  
      def __init__(self, cond: Expression, if_expr: Expression, else_expr: Expression) -> None:
          super().__init__()
          self.cond = cond
          self.if_expr = if_expr
          self.else_expr = else_expr
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_conditional_expr(self)
  
  
  class BackquoteExpr(Expression):
      """Python 2 expression `...`."""
  
      expr = None  # type: Expression
  
      def __init__(self, expr: Expression) -> None:
          super().__init__()
          self.expr = expr
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_backquote_expr(self)
  
  
  class TypeApplication(Expression):
      """Type application expr[type, ...]"""
  
      expr = None  # type: Expression
      types = None  # type: List[mypy.types.Type]
  
      def __init__(self, expr: Expression, types: List['mypy.types.Type']) -> None:
          super().__init__()
          self.expr = expr
          self.types = types
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_type_application(self)
  
  
  # Variance of a type variable. For example, T in the definition of
  # List[T] is invariant, so List[int] is not a subtype of List[object],
  # and also List[object] is not a subtype of List[int].
  #
  # The T in Iterable[T] is covariant, so Iterable[int] is a subtype of
  # Iterable[object], but not vice versa.
  #
  # If T is contravariant in Foo[T], Foo[object] is a subtype of
  # Foo[int], but not vice versa.
  INVARIANT = 0  # type: Final[int]
  COVARIANT = 1  # type: Final[int]
  CONTRAVARIANT = 2  # type: Final[int]
  
  
  class TypeVarLikeExpr(SymbolNode, Expression):
      """Base class for TypeVarExpr and ParamSpecExpr."""
      _name = ''
      _fullname = ''
      # Upper bound: only subtypes of upper_bound are valid as values. By default
      # this is 'object', meaning no restriction.
      upper_bound = None  # type: mypy.types.Type
      # Variance of the type variable. Invariant is the default.
      # TypeVar(..., covariant=True) defines a covariant type variable.
      # TypeVar(..., contravariant=True) defines a contravariant type
      # variable.
      variance = INVARIANT
  
      def __init__(
          self, name: str, fullname: str, upper_bound: 'mypy.types.Type', variance: int = INVARIANT
      ) -> None:
          super().__init__()
          self._name = name
          self._fullname = fullname
          self.upper_bound = upper_bound
          self.variance = variance
  
      @property
      def name(self) -> str:
          return self._name
  
      @property
      def fullname(self) -> str:
          return self._fullname
  
  
  class TypeVarExpr(TypeVarLikeExpr):
      """Type variable expression TypeVar(...).
  
      This is also used to represent type variables in symbol tables.
  
      A type variable is not valid as a type unless bound in a TypeVarLikeScope.
      That happens within:
  
       1. a generic class that uses the type variable as a type argument or
       2. a generic function that refers to the type variable in its signature.
      """
      # Value restriction: only types in the list are valid as values. If the
      # list is empty, there is no restriction.
      values = None  # type: List[mypy.types.Type]
  
      def __init__(self, name: str, fullname: str,
                   values: List['mypy.types.Type'],
                   upper_bound: 'mypy.types.Type',
                   variance: int = INVARIANT) -> None:
          super().__init__(name, fullname, upper_bound, variance)
          self.values = values
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_type_var_expr(self)
  
      def serialize(self) -> JsonDict:
          return {'.class': 'TypeVarExpr',
                  'name': self._name,
                  'fullname': self._fullname,
                  'values': [t.serialize() for t in self.values],
                  'upper_bound': self.upper_bound.serialize(),
                  'variance': self.variance,
                  }
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'TypeVarExpr':
          assert data['.class'] == 'TypeVarExpr'
          return TypeVarExpr(data['name'],
                             data['fullname'],
                             [mypy.types.deserialize_type(v) for v in data['values']],
                             mypy.types.deserialize_type(data['upper_bound']),
                             data['variance'])
  
  
  class ParamSpecExpr(TypeVarLikeExpr):
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_paramspec_expr(self)
  
      def serialize(self) -> JsonDict:
          return {
              '.class': 'ParamSpecExpr',
              'name': self._name,
              'fullname': self._fullname,
              'upper_bound': self.upper_bound.serialize(),
              'variance': self.variance,
          }
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'ParamSpecExpr':
          assert data['.class'] == 'ParamSpecExpr'
          return ParamSpecExpr(
              data['name'],
              data['fullname'],
              mypy.types.deserialize_type(data['upper_bound']),
              data['variance']
          )
  
  
  class TypeAliasExpr(Expression):
      """Type alias expression (rvalue)."""
  
      # The target type.
      type = None  # type: mypy.types.Type
      # Names of unbound type variables used to define the alias
      tvars = None  # type: List[str]
      # Whether this alias was defined in bare form. Used to distinguish
      # between
      #     A = List
      # and
      #     A = List[Any]
      no_args = False  # type: bool
  
      def __init__(self, node: 'TypeAlias') -> None:
          super().__init__()
          self.type = node.target
          self.tvars = node.alias_tvars
          self.no_args = node.no_args
          self.node = node
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_type_alias_expr(self)
  
  
  class NamedTupleExpr(Expression):
      """Named tuple expression namedtuple(...) or NamedTuple(...)."""
  
      # The class representation of this named tuple (its tuple_type attribute contains
      # the tuple item types)
      info = None  # type: TypeInfo
      is_typed = False  # whether this class was created with typing.NamedTuple
  
      def __init__(self, info: 'TypeInfo', is_typed: bool = False) -> None:
          super().__init__()
          self.info = info
          self.is_typed = is_typed
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_namedtuple_expr(self)
  
  
  class TypedDictExpr(Expression):
      """Typed dict expression TypedDict(...)."""
  
      # The class representation of this typed dict
      info = None  # type: TypeInfo
  
      def __init__(self, info: 'TypeInfo') -> None:
          super().__init__()
          self.info = info
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_typeddict_expr(self)
  
  
  class EnumCallExpr(Expression):
      """Named tuple expression Enum('name', 'val1 val2 ...')."""
  
      # The class representation of this enumerated type
      info = None  # type: TypeInfo
      # The item names (for debugging)
      items = None  # type: List[str]
      values = None  # type: List[Optional[Expression]]
  
      def __init__(self, info: 'TypeInfo', items: List[str],
                   values: List[Optional[Expression]]) -> None:
          super().__init__()
          self.info = info
          self.items = items
          self.values = values
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_enum_call_expr(self)
  
  
  class PromoteExpr(Expression):
      """Ducktype class decorator expression _promote(...)."""
  
      type = None  # type: mypy.types.Type
  
      def __init__(self, type: 'mypy.types.Type') -> None:
          super().__init__()
          self.type = type
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit__promote_expr(self)
  
  
  class NewTypeExpr(Expression):
      """NewType expression NewType(...)."""
      name = None  # type: str
      # The base type (the second argument to NewType)
      old_type = None  # type: Optional[mypy.types.Type]
      # The synthesized class representing the new type (inherits old_type)
      info = None  # type: Optional[TypeInfo]
  
      def __init__(self, name: str, old_type: 'Optional[mypy.types.Type]', line: int,
                   column: int) -> None:
          super().__init__()
          self.name = name
          self.old_type = old_type
          self.line = line
          self.column = column
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_newtype_expr(self)
  
  
  class AwaitExpr(Expression):
      """Await expression (await ...)."""
  
      expr = None  # type: Expression
  
      def __init__(self, expr: Expression) -> None:
          super().__init__()
          self.expr = expr
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_await_expr(self)
  
  
  # Constants
  
  
  class TempNode(Expression):
      """Temporary dummy node used during type checking.
  
      This node is not present in the original program; it is just an artifact
      of the type checker implementation. It only represents an opaque node with
      some fixed type.
      """
  
      type = None  # type: mypy.types.Type
      # Is this TempNode used to indicate absence of a right hand side in an annotated assignment?
      # (e.g. for 'x: int' the rvalue is TempNode(AnyType(TypeOfAny.special_form), no_rhs=True))
      no_rhs = False  # type: bool
  
      def __init__(self,
                   typ: 'mypy.types.Type',
                   no_rhs: bool = False,
                   *,
                   context: Optional[Context] = None) -> None:
          """Construct a dummy node; optionally borrow line/column from context object."""
          super().__init__()
          self.type = typ
          self.no_rhs = no_rhs
          if context is not None:
              self.line = context.line
              self.column = context.column
  
      def __repr__(self) -> str:
          return 'TempNode:%d(%s)' % (self.line, str(self.type))
  
      def accept(self, visitor: ExpressionVisitor[T]) -> T:
          return visitor.visit_temp_node(self)
  
  
  class TypeInfo(SymbolNode):
      """The type structure of a single class.
  
      Each TypeInfo corresponds one-to-one to a ClassDef, which
      represents the AST of the class.
  
      In type-theory terms, this is a "type constructor", and if the
      class is generic then it will be a type constructor of higher kind.
      Where the class is used in an actual type, it's in the form of an
      Instance, which amounts to a type application of the tycon to
      the appropriate number of arguments.
      """
  
      _fullname = None  # type: Bogus[str]          # Fully qualified name
      # Fully qualified name for the module this type was defined in. This
      # information is also in the fullname, but is harder to extract in the
      # case of nested class definitions.
      module_name = None  # type: str
      defn = None  # type: ClassDef          # Corresponding ClassDef
      # Method Resolution Order: the order of looking up attributes. The first
      # value always to refers to this class.
      mro = None  # type: List[TypeInfo]
      # Used to stash the names of the mro classes temporarily between
      # deserialization and fixup. See deserialize() for why.
      _mro_refs = None  # type: Optional[List[str]]
      bad_mro = False  # Could not construct full MRO
  
      declared_metaclass = None  # type: Optional[mypy.types.Instance]
      metaclass_type = None  # type: Optional[mypy.types.Instance]
  
      names = None  # type: SymbolTable      # Names defined directly in this type
      is_abstract = False                    # Does the class have any abstract attributes?
      is_protocol = False                    # Is this a protocol class?
      runtime_protocol = False               # Does this protocol support isinstance checks?
      abstract_attributes = None  # type: List[str]
  
      # The attributes 'assuming' and 'assuming_proper' represent structural subtype matrices.
      #
      # In languages with structural subtyping, one can keep a global subtype matrix like this:
      #   . A B C .
      #   A 1 0 0
      #   B 1 1 1
      #   C 1 0 1
      #   .
      # where 1 indicates that the type in corresponding row is a subtype of the type
      # in corresponding column. This matrix typically starts filled with all 1's and
      # a typechecker tries to "disprove" every subtyping relation using atomic (or nominal) types.
      # However, we don't want to keep this huge global state. Instead, we keep the subtype
      # information in the form of list of pairs (subtype, supertype) shared by all 'Instance's
      # with given supertype's TypeInfo. When we enter a subtype check we push a pair in this list
      # thus assuming that we started with 1 in corresponding matrix element. Such algorithm allows
      # to treat recursive and mutually recursive protocols and other kinds of complex situations.
      #
      # If concurrent/parallel type checking will be added in future,
      # then there should be one matrix per thread/process to avoid false negatives
      # during the type checking phase.
      assuming = None  # type: List[Tuple[mypy.types.Instance, mypy.types.Instance]]
      assuming_proper = None  # type: List[Tuple[mypy.types.Instance, mypy.types.Instance]]
      # Ditto for temporary 'inferring' stack of recursive constraint inference.
      # It contains Instance's of protocol types that appeared as an argument to
      # constraints.infer_constraints(). We need 'inferring' to avoid infinite recursion for
      # recursive and mutually recursive protocols.
      #
      # We make 'assuming' and 'inferring' attributes here instead of passing they as kwargs,
      # since this would require to pass them in many dozens of calls. In particular,
      # there is a dependency infer_constraint -> is_subtype -> is_callable_subtype ->
      # -> infer_constraints.
      inferring = None  # type: List[mypy.types.Instance]
      # 'inferring' and 'assuming' can't be made sets, since we need to use
      # is_same_type to correctly treat unions.
  
      # Classes inheriting from Enum shadow their true members with a __getattr__, so we
      # have to treat them as a special case.
      is_enum = False
      # If true, any unknown attributes should have type 'Any' instead
      # of generating a type error.  This would be true if there is a
      # base class with type 'Any', but other use cases may be
      # possible. This is similar to having __getattr__ that returns Any
      # (and __setattr__), but without the __getattr__ method.
      fallback_to_any = False
  
      # Information related to type annotations.
  
      # Generic type variable names (full names)
      type_vars = None  # type: List[str]
  
      # Direct base classes.
      bases = None  # type: List[mypy.types.Instance]
  
      # Another type which this type will be treated as a subtype of,
      # even though it's not a subclass in Python.  The non-standard
      # `@_promote` decorator introduces this, and there are also
      # several builtin examples, in particular `int` -> `float`.
      _promote = None  # type: Optional[mypy.types.Type]
  
      # Representation of a Tuple[...] base class, if the class has any
      # (e.g., for named tuples). If this is not None, the actual Type
      # object used for this class is not an Instance but a TupleType;
      # the corresponding Instance is set as the fallback type of the
      # tuple type.
      tuple_type = None  # type: Optional[mypy.types.TupleType]
  
      # Is this a named tuple type?
      is_named_tuple = False
  
      # If this class is defined by the TypedDict type constructor,
      # then this is not None.
      typeddict_type = None  # type: Optional[mypy.types.TypedDictType]
  
      # Is this a newtype type?
      is_newtype = False
  
      # Is this a synthesized intersection type?
      is_intersection = False
  
      # This is a dictionary that will be serialized and un-serialized as is.
      # It is useful for plugins to add their data to save in the cache.
      metadata = None  # type: Dict[str, JsonDict]
  
      FLAGS = [
          'is_abstract', 'is_enum', 'fallback_to_any', 'is_named_tuple',
          'is_newtype', 'is_protocol', 'runtime_protocol', 'is_final',
          'is_intersection',
      ]  # type: Final[List[str]]
  
      def __init__(self, names: 'SymbolTable', defn: ClassDef, module_name: str) -> None:
          """Initialize a TypeInfo."""
          super().__init__()
          self.names = names
          self.defn = defn
          self.module_name = module_name
          self.type_vars = []
          self.bases = []
          self.mro = []
          self._fullname = defn.fullname
          self.is_abstract = False
          self.abstract_attributes = []
          self.assuming = []
          self.assuming_proper = []
          self.inferring = []
          self.add_type_vars()
          self.metadata = {}
          self.is_final = False
  
      def add_type_vars(self) -> None:
          if self.defn.type_vars:
              for vd in self.defn.type_vars:
                  self.type_vars.append(vd.fullname)
  
      @property
      def name(self) -> str:
          """Short name."""
          return self.defn.name
  
      @property
      def fullname(self) -> Bogus[str]:
          return self._fullname
  
      def is_generic(self) -> bool:
          """Is the type generic (i.e. does it have type variables)?"""
          return len(self.type_vars) > 0
  
      def get(self, name: str) -> 'Optional[SymbolTableNode]':
          for cls in self.mro:
              n = cls.names.get(name)
              if n:
                  return n
          return None
  
      def get_containing_type_info(self, name: str) -> 'Optional[TypeInfo]':
          for cls in self.mro:
              if name in cls.names:
                  return cls
          return None
  
      @property
      def protocol_members(self) -> List[str]:
          # Protocol members are names of all attributes/methods defined in a protocol
          # and in all its supertypes (except for 'object').
          members = set()  # type: Set[str]
          assert self.mro, "This property can be only accessed after MRO is (re-)calculated"
          for base in self.mro[:-1]:  # we skip "object" since everyone implements it
              if base.is_protocol:
                  for name in base.names:
                      members.add(name)
          return sorted(list(members))
  
      def __getitem__(self, name: str) -> 'SymbolTableNode':
          n = self.get(name)
          if n:
              return n
          else:
              raise KeyError(name)
  
      def __repr__(self) -> str:
          return '<TypeInfo %s>' % self.fullname
  
      def __bool__(self) -> bool:
          # We defined this here instead of just overriding it in
          # FakeInfo so that mypyc can generate a direct call instead of
          # using the generic bool handling.
          return not isinstance(self, FakeInfo)
  
      def has_readable_member(self, name: str) -> bool:
          return self.get(name) is not None
  
      def get_method(self, name: str) -> Optional[FuncBase]:
          for cls in self.mro:
              if name in cls.names:
                  node = cls.names[name].node
                  if isinstance(node, FuncBase):
                      return node
                  else:
                      return None
          return None
  
      def calculate_metaclass_type(self) -> 'Optional[mypy.types.Instance]':
          declared = self.declared_metaclass
          if declared is not None and not declared.type.has_base('builtins.type'):
              return declared
          if self._fullname == 'builtins.type':
              return mypy.types.Instance(self, [])
          candidates = [s.declared_metaclass
                        for s in self.mro
                        if s.declared_metaclass is not None
                        and s.declared_metaclass.type is not None]
          for c in candidates:
              if all(other.type in c.type.mro for other in candidates):
                  return c
          return None
  
      def is_metaclass(self) -> bool:
          return (self.has_base('builtins.type') or self.fullname == 'abc.ABCMeta' or
                  self.fallback_to_any)
  
      def has_base(self, fullname: str) -> bool:
          """Return True if type has a base type with the specified name.
  
          This can be either via extension or via implementation.
          """
          for cls in self.mro:
              if cls.fullname == fullname:
                  return True
          return False
  
      def direct_base_classes(self) -> 'List[TypeInfo]':
          """Return a direct base classes.
  
          Omit base classes of other base classes.
          """
          return [base.type for base in self.bases]
  
      def __str__(self) -> str:
          """Return a string representation of the type.
  
          This includes the most important information about the type.
          """
          return self.dump()
  
      def dump(self,
               str_conv: 'Optional[mypy.strconv.StrConv]' = None,
               type_str_conv: 'Optional[mypy.types.TypeStrVisitor]' = None) -> str:
          """Return a string dump of the contents of the TypeInfo."""
          if not str_conv:
              str_conv = mypy.strconv.StrConv()
          base = ''  # type: str
  
          def type_str(typ: 'mypy.types.Type') -> str:
              if type_str_conv:
                  return typ.accept(type_str_conv)
              return str(typ)
  
          head = 'TypeInfo' + str_conv.format_id(self)
          if self.bases:
              base = 'Bases({})'.format(', '.join(type_str(base)
                                                  for base in self.bases))
          mro = 'Mro({})'.format(', '.join(item.fullname + str_conv.format_id(item)
                                           for item in self.mro))
          names = []
          for name in sorted(self.names):
              description = name + str_conv.format_id(self.names[name].node)
              node = self.names[name].node
              if isinstance(node, Var) and node.type:
                  description += ' ({})'.format(type_str(node.type))
              names.append(description)
          items = [
              'Name({})'.format(self.fullname),
              base,
              mro,
              ('Names', names),
          ]
          if self.declared_metaclass:
              items.append('DeclaredMetaclass({})'.format(type_str(self.declared_metaclass)))
          if self.metaclass_type:
              items.append('MetaclassType({})'.format(type_str(self.metaclass_type)))
          return mypy.strconv.dump_tagged(
              items,
              head,
              str_conv=str_conv)
  
      def serialize(self) -> JsonDict:
          # NOTE: This is where all ClassDefs originate, so there shouldn't be duplicates.
          data = {'.class': 'TypeInfo',
                  'module_name': self.module_name,
                  'fullname': self.fullname,
                  'names': self.names.serialize(self.fullname),
                  'defn': self.defn.serialize(),
                  'abstract_attributes': self.abstract_attributes,
                  'type_vars': self.type_vars,
                  'bases': [b.serialize() for b in self.bases],
                  'mro': [c.fullname for c in self.mro],
                  '_promote': None if self._promote is None else self._promote.serialize(),
                  'declared_metaclass': (None if self.declared_metaclass is None
                                         else self.declared_metaclass.serialize()),
                  'metaclass_type':
                      None if self.metaclass_type is None else self.metaclass_type.serialize(),
                  'tuple_type': None if self.tuple_type is None else self.tuple_type.serialize(),
                  'typeddict_type':
                      None if self.typeddict_type is None else self.typeddict_type.serialize(),
                  'flags': get_flags(self, TypeInfo.FLAGS),
                  'metadata': self.metadata,
                  }
          return data
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'TypeInfo':
          names = SymbolTable.deserialize(data['names'])
          defn = ClassDef.deserialize(data['defn'])
          module_name = data['module_name']
          ti = TypeInfo(names, defn, module_name)
          ti._fullname = data['fullname']
          # TODO: Is there a reason to reconstruct ti.subtypes?
          ti.abstract_attributes = data['abstract_attributes']
          ti.type_vars = data['type_vars']
          ti.bases = [mypy.types.Instance.deserialize(b) for b in data['bases']]
          ti._promote = (None if data['_promote'] is None
                         else mypy.types.deserialize_type(data['_promote']))
          ti.declared_metaclass = (None if data['declared_metaclass'] is None
                                   else mypy.types.Instance.deserialize(data['declared_metaclass']))
          ti.metaclass_type = (None if data['metaclass_type'] is None
                               else mypy.types.Instance.deserialize(data['metaclass_type']))
          # NOTE: ti.mro will be set in the fixup phase based on these
          # names.  The reason we need to store the mro instead of just
          # recomputing it from base classes has to do with a subtle
          # point about fine-grained incremental: the cache files might
          # not be loaded until after a class in the mro has changed its
          # bases, which causes the mro to change. If we recomputed our
          # mro, we would compute the *new* mro, which leaves us with no
          # way to detect that the mro has changed! Thus we need to make
          # sure to load the original mro so that once the class is
          # rechecked, it can tell that the mro has changed.
          ti._mro_refs = data['mro']
          ti.tuple_type = (None if data['tuple_type'] is None
                           else mypy.types.TupleType.deserialize(data['tuple_type']))
          ti.typeddict_type = (None if data['typeddict_type'] is None
                              else mypy.types.TypedDictType.deserialize(data['typeddict_type']))
          ti.metadata = data['metadata']
          set_flags(ti, data['flags'])
          return ti
  
  
  class FakeInfo(TypeInfo):
      # types.py defines a single instance of this class, called types.NOT_READY.
      # This instance is used as a temporary placeholder in the process of de-serialization
      # of 'Instance' types. The de-serialization happens in two steps: In the first step,
      # Instance.type is set to NOT_READY. In the second step (in fixup.py) it is replaced by
      # an actual TypeInfo. If you see the assertion error below, then most probably something
      # went wrong during the second step and an 'Instance' that raised this error was not fixed.
      # Note:
      # 'None' is not used as a dummy value for two reasons:
      # 1. This will require around 80-100 asserts to make 'mypy --strict-optional mypy'
      #    pass cleanly.
      # 2. If NOT_READY value is accidentally used somewhere, it will be obvious where the value
      #    is from, whereas a 'None' value could come from anywhere.
      #
      # Additionally, this serves as a more general-purpose placeholder
      # for missing TypeInfos in a number of places where the excuses
      # for not being Optional are a little weaker.
      #
      # TypeInfo defines a __bool__ method that returns False for FakeInfo
      # so that it can be conveniently tested against in the same way that it
      # would be if things were properly optional.
      def __init__(self, msg: str) -> None:
          self.msg = msg
  
      def __getattribute__(self, attr: str) -> None:
          # Handle __class__ so that isinstance still works...
          if attr == '__class__':
              return object.__getattribute__(self, attr)
          raise AssertionError(object.__getattribute__(self, 'msg'))
  
  
  VAR_NO_INFO = FakeInfo('Var is lacking info')  # type: Final[TypeInfo]
  CLASSDEF_NO_INFO = FakeInfo('ClassDef is lacking info')  # type: Final[TypeInfo]
  FUNC_NO_INFO = FakeInfo('FuncBase for non-methods lack info')  # type: Final[TypeInfo]
  
  
  class TypeAlias(SymbolNode):
      """
      A symbol node representing a type alias.
  
      Type alias is a static concept, in contrast to variables with types
      like Type[...]. Namely:
          * type aliases
              - can be used in type context (annotations)
              - cannot be re-assigned
          * variables with type Type[...]
              - cannot be used in type context
              - but can be re-assigned
  
      An alias can be defined only by an assignment to a name (not any other lvalues).
  
      Such assignment defines an alias by default. To define a variable,
      an explicit Type[...] annotation is required. As an exception,
      at non-global scope non-subscripted rvalue creates a variable even without
      an annotation. This exception exists to accommodate the common use case of
      class-valued attributes. See SemanticAnalyzerPass2.check_and_set_up_type_alias
      for details.
  
      Aliases can be generic. Currently, mypy uses unbound type variables for
      generic aliases and identifies them by name. Essentially, type aliases
      work as macros that expand textually. The definition and expansion rules are
      following:
  
          1. An alias targeting a generic class without explicit variables act as
          the given class (this doesn't apply to Tuple and Callable, which are not proper
          classes but special type constructors):
  
              A = List
              AA = List[Any]
  
              x: A  # same as List[Any]
              x: A[int]  # same as List[int]
  
              x: AA  # same as List[Any]
              x: AA[int]  # Error!
  
              C = Callable  # Same as Callable[..., Any]
              T = Tuple  # Same as Tuple[Any, ...]
  
          2. An alias using explicit type variables in its rvalue expects
          replacements (type arguments) for these variables. If missing, they
          are treated as Any, like for other generics:
  
              B = List[Tuple[T, T]]
  
              x: B  # same as List[Tuple[Any, Any]]
              x: B[int]  # same as List[Tuple[int, int]]
  
              def f(x: B[T]) -> T: ...  # without T, Any would be used here
  
          3. An alias can be defined using another aliases. In the definition
          rvalue the Any substitution doesn't happen for top level unsubscripted
          generic classes:
  
              A = List
              B = A  # here A is expanded to List, _not_ List[Any],
                     # to match the Python runtime behaviour
              x: B[int]  # same as List[int]
              C = List[A]  # this expands to List[List[Any]]
  
              AA = List[T]
              D = AA  # here AA expands to List[Any]
              x: D[int]  # Error!
  
      Note: the fact that we support aliases like `A = List` means that the target
      type will be initially an instance type with wrong number of type arguments.
      Such instances are all fixed in the third pass of semantic analyzis.
      We therefore store the difference between `List` and `List[Any]` rvalues (targets)
      using the `no_args` flag. See also TypeAliasExpr.no_args.
  
      Meaning of other fields:
  
      target: The target type. For generic aliases contains unbound type variables
          as nested types.
      _fullname: Qualified name of this type alias. This is used in particular
          to track fine grained dependencies from aliases.
      alias_tvars: Names of unbound type variables used to define this alias.
      normalized: Used to distinguish between `A = List`, and `A = list`. Both
          are internally stored using `builtins.list` (because `typing.List` is
          itself an alias), while the second cannot be subscripted because of
          Python runtime limitation.
      line and column: Line an column on the original alias definition.
      """
      __slots__ = ('target', '_fullname', 'alias_tvars', 'no_args', 'normalized',
                   'line', 'column', '_is_recursive')
  
      def __init__(self, target: 'mypy.types.Type', fullname: str, line: int, column: int,
                   *,
                   alias_tvars: Optional[List[str]] = None,
                   no_args: bool = False,
                   normalized: bool = False) -> None:
          self._fullname = fullname
          self.target = target
          if alias_tvars is None:
              alias_tvars = []
          self.alias_tvars = alias_tvars
          self.no_args = no_args
          self.normalized = normalized
          # This attribute is manipulated by TypeAliasType. If non-None,
          # it is the cached value.
          self._is_recursive = None  # type: Optional[bool]
          super().__init__(line, column)
  
      @property
      def name(self) -> str:
          return self._fullname.split('.')[-1]
  
      @property
      def fullname(self) -> str:
          return self._fullname
  
      def serialize(self) -> JsonDict:
          data = {'.class': 'TypeAlias',
                  'fullname': self._fullname,
                  'target': self.target.serialize(),
                  'alias_tvars': self.alias_tvars,
                  'no_args': self.no_args,
                  'normalized': self.normalized,
                  'line': self.line,
                  'column': self.column
                  }  # type: JsonDict
          return data
  
      def accept(self, visitor: NodeVisitor[T]) -> T:
          return visitor.visit_type_alias(self)
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'TypeAlias':
          assert data['.class'] == 'TypeAlias'
          fullname = data['fullname']
          alias_tvars = data['alias_tvars']
          target = mypy.types.deserialize_type(data['target'])
          no_args = data['no_args']
          normalized = data['normalized']
          line = data['line']
          column = data['column']
          return cls(target, fullname, line, column, alias_tvars=alias_tvars,
                     no_args=no_args, normalized=normalized)
  
  
  class PlaceholderNode(SymbolNode):
      """Temporary symbol node that will later become a real SymbolNode.
  
      These are only present during semantic analysis when using the new
      semantic analyzer. These are created if some essential dependencies
      of a definition are not yet complete.
  
      A typical use is for names imported from a module which is still
      incomplete (within an import cycle):
  
        from m import f  # Initially may create PlaceholderNode
  
      This is particularly important if the imported shadows a name from
      an enclosing scope or builtins:
  
        from m import int  # Placeholder avoids mixups with builtins.int
  
      Another case where this is useful is when there is another definition
      or assignment:
  
        from m import f
        def f() -> None: ...
  
      In the above example, the presence of PlaceholderNode allows us to
      handle the second definition as a redefinition.
  
      They are also used to create PlaceholderType instances for types
      that refer to incomplete types. Example:
  
        class C(Sequence[C]): ...
  
      We create a PlaceholderNode (with becomes_typeinfo=True) for C so
      that the type C in Sequence[C] can be bound.
  
      Attributes:
  
        fullname: Full name of of the PlaceholderNode.
        node: AST node that contains the definition that caused this to
            be created. This is useful for tracking order of incomplete definitions
            and for debugging.
        becomes_typeinfo: If True, this refers something that could later
            become a TypeInfo. It can't be used with type variables, in
            particular, as this would cause issues with class type variable
            detection.
  
      The long-term purpose of placeholder nodes/types is to evolve into
      something that can support general recursive types.
      """
  
      def __init__(self, fullname: str, node: Node, line: int, *,
                   becomes_typeinfo: bool = False) -> None:
          self._fullname = fullname
          self.node = node
          self.becomes_typeinfo = becomes_typeinfo
          self.line = line
  
      @property
      def name(self) -> str:
          return self._fullname.split('.')[-1]
  
      @property
      def fullname(self) -> str:
          return self._fullname
  
      def serialize(self) -> JsonDict:
          assert False, "PlaceholderNode can't be serialized"
  
      def accept(self, visitor: NodeVisitor[T]) -> T:
          return visitor.visit_placeholder_node(self)
  
  
  class SymbolTableNode:
      """Description of a name binding in a symbol table.
  
      These are only used as values in module (global), function (local)
      and class symbol tables (see SymbolTable). The name that is bound is
      the key in SymbolTable.
  
      Symbol tables don't contain direct references to AST nodes primarily
      because there can be multiple symbol table references to a single
      AST node (due to imports and aliases), and different references can
      behave differently. This class describes the unique properties of
      each reference.
  
      The most fundamental attribute is 'node', which is the AST node that
      the name refers to.
  
      The kind is usually one of LDEF, GDEF or MDEF, depending on the scope
      of the definition. These three kinds can usually be used
      interchangeably and the difference between local, global and class
      scopes is mostly descriptive, with no semantic significance.
      However, some tools that consume mypy ASTs may care about these so
      they should be correct.
  
      Attributes:
          node: AST node of definition. Among others, this can be one of
              FuncDef, Var, TypeInfo, TypeVarExpr or MypyFile -- or None
              for cross_ref that hasn't been fixed up yet.
          kind: Kind of node. Possible values:
                 - LDEF: local definition
                 - GDEF: global (module-level) definition
                 - MDEF: class member definition
                 - UNBOUND_IMPORTED: temporary kind for imported names (we
                   don't know the final kind yet)
          module_public: If False, this name won't be imported via
              'from <module> import *'. This has no effect on names within
              classes.
          module_hidden: If True, the name will be never exported (needed for
              stub files)
          cross_ref: For deserialized MypyFile nodes, the referenced module
              name; for other nodes, optionally the name of the referenced object.
          implicit: Was this defined by assignment to self attribute?
          plugin_generated: Was this symbol generated by a plugin?
              (And therefore needs to be removed in aststrip.)
          no_serialize: Do not serialize this node if True. This is used to prevent
              keys in the cache that refer to modules on which this file does not
              depend. Currently this can happen if there is a module not in build
              used e.g. like this:
                  import a.b.c # type: ignore
              This will add a submodule symbol to parent module `a` symbol table,
              but `a.b` is _not_ added as its dependency. Therefore, we should
              not serialize these symbols as they may not be found during fixup
              phase, instead they will be re-added during subsequent patch parents
              phase.
              TODO: Refactor build.py to make dependency tracking more transparent
              and/or refactor look-up functions to not require parent patching.
  
      NOTE: No other attributes should be added to this class unless they
      are shared by all node kinds.
      """
  
      __slots__ = ('kind',
                   'node',
                   'module_public',
                   'module_hidden',
                   'cross_ref',
                   'implicit',
                   'plugin_generated',
                   'no_serialize',
                   )
  
      def __init__(self,
                   kind: int,
                   node: Optional[SymbolNode],
                   module_public: bool = True,
                   implicit: bool = False,
                   module_hidden: bool = False,
                   *,
                   plugin_generated: bool = False,
                   no_serialize: bool = False) -> None:
          self.kind = kind
          self.node = node
          self.module_public = module_public
          self.implicit = implicit
          self.module_hidden = module_hidden
          self.cross_ref = None  # type: Optional[str]
          self.plugin_generated = plugin_generated
          self.no_serialize = no_serialize
  
      @property
      def fullname(self) -> Optional[str]:
          if self.node is not None:
              return self.node.fullname
          else:
              return None
  
      @property
      def type(self) -> 'Optional[mypy.types.Type]':
          node = self.node
          if isinstance(node, (Var, SYMBOL_FUNCBASE_TYPES)) and node.type is not None:
              return node.type
          elif isinstance(node, Decorator):
              return node.var.type
          else:
              return None
  
      def copy(self) -> 'SymbolTableNode':
          new = SymbolTableNode(self.kind,
                                self.node,
                                self.module_public,
                                self.implicit,
                                self.module_hidden)
          new.cross_ref = self.cross_ref
          return new
  
      def __str__(self) -> str:
          s = '{}/{}'.format(node_kinds[self.kind], short_type(self.node))
          if isinstance(self.node, SymbolNode):
              s += ' ({})'.format(self.node.fullname)
          # Include declared type of variables and functions.
          if self.type is not None:
              s += ' : {}'.format(self.type)
          return s
  
      def serialize(self, prefix: str, name: str) -> JsonDict:
          """Serialize a SymbolTableNode.
  
          Args:
            prefix: full name of the containing module or class; or None
            name: name of this object relative to the containing object
          """
          data = {'.class': 'SymbolTableNode',
                  'kind': node_kinds[self.kind],
                  }  # type: JsonDict
          if self.module_hidden:
              data['module_hidden'] = True
          if not self.module_public:
              data['module_public'] = False
          if self.implicit:
              data['implicit'] = True
          if self.plugin_generated:
              data['plugin_generated'] = True
          if isinstance(self.node, MypyFile):
              data['cross_ref'] = self.node.fullname
          else:
              assert self.node is not None, '%s:%s' % (prefix, name)
              if prefix is not None:
                  fullname = self.node.fullname
                  if (fullname is not None and '.' in fullname
                          and fullname != prefix + '.' + name
                          and not (isinstance(self.node, Var)
                                   and self.node.from_module_getattr)):
                      assert not isinstance(self.node, PlaceholderNode)
                      data['cross_ref'] = fullname
                      return data
              data['node'] = self.node.serialize()
          return data
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'SymbolTableNode':
          assert data['.class'] == 'SymbolTableNode'
          kind = inverse_node_kinds[data['kind']]
          if 'cross_ref' in data:
              # This will be fixed up later.
              stnode = SymbolTableNode(kind, None)
              stnode.cross_ref = data['cross_ref']
          else:
              assert 'node' in data, data
              node = SymbolNode.deserialize(data['node'])
              stnode = SymbolTableNode(kind, node)
          if 'module_hidden' in data:
              stnode.module_hidden = data['module_hidden']
          if 'module_public' in data:
              stnode.module_public = data['module_public']
          if 'implicit' in data:
              stnode.implicit = data['implicit']
          if 'plugin_generated' in data:
              stnode.plugin_generated = data['plugin_generated']
          return stnode
  
  
  class SymbolTable(Dict[str, SymbolTableNode]):
      """Static representation of a namespace dictionary.
  
      This is used for module, class and function namespaces.
      """
  
      def __str__(self) -> str:
          a = []  # type: List[str]
          for key, value in self.items():
              # Filter out the implicit import of builtins.
              if isinstance(value, SymbolTableNode):
                  if (value.fullname != 'builtins' and
                          (value.fullname or '').split('.')[-1] not in
                          implicit_module_attrs):
                      a.append('  ' + str(key) + ' : ' + str(value))
              else:
                  a.append('  <invalid item>')
          a = sorted(a)
          a.insert(0, 'SymbolTable(')
          a[-1] += ')'
          return '\n'.join(a)
  
      def copy(self) -> 'SymbolTable':
          return SymbolTable([(key, node.copy())
                              for key, node in self.items()])
  
      def serialize(self, fullname: str) -> JsonDict:
          data = {'.class': 'SymbolTable'}  # type: JsonDict
          for key, value in self.items():
              # Skip __builtins__: it's a reference to the builtins
              # module that gets added to every module by
              # SemanticAnalyzerPass2.visit_file(), but it shouldn't be
              # accessed by users of the module.
              if key == '__builtins__' or value.no_serialize:
                  continue
              data[key] = value.serialize(fullname, key)
          return data
  
      @classmethod
      def deserialize(cls, data: JsonDict) -> 'SymbolTable':
          assert data['.class'] == 'SymbolTable'
          st = SymbolTable()
          for key, value in data.items():
              if key != '.class':
                  st[key] = SymbolTableNode.deserialize(value)
          return st
  
  
  def get_flags(node: Node, names: List[str]) -> List[str]:
      return [name for name in names if getattr(node, name)]
  
  
  def set_flags(node: Node, flags: List[str]) -> None:
      for name in flags:
          setattr(node, name, True)
  
  
  def get_member_expr_fullname(expr: MemberExpr) -> Optional[str]:
      """Return the qualified name representation of a member expression.
  
      Return a string of form foo.bar, foo.bar.baz, or similar, or None if the
      argument cannot be represented in this form.
      """
      initial = None  # type: Optional[str]
      if isinstance(expr.expr, NameExpr):
          initial = expr.expr.name
      elif isinstance(expr.expr, MemberExpr):
          initial = get_member_expr_fullname(expr.expr)
      else:
          return None
      return '{}.{}'.format(initial, expr.name)
  
  
  deserialize_map = {
      key: obj.deserialize
      for key, obj in globals().items()
      if type(obj) is not FakeInfo
      and isinstance(obj, type) and issubclass(obj, SymbolNode) and obj is not SymbolNode
  }  # type: Final
  
  
  def check_arg_kinds(arg_kinds: List[int], nodes: List[T], fail: Callable[[str, T], None]) -> None:
      is_var_arg = False
      is_kw_arg = False
      seen_named = False
      seen_opt = False
      for kind, node in zip(arg_kinds, nodes):
          if kind == ARG_POS:
              if is_var_arg or is_kw_arg or seen_named or seen_opt:
                  fail("Required positional args may not appear "
                       "after default, named or var args",
                       node)
                  break
          elif kind == ARG_OPT:
              if is_var_arg or is_kw_arg or seen_named:
                  fail("Positional default args may not appear after named or var args", node)
                  break
              seen_opt = True
          elif kind == ARG_STAR:
              if is_var_arg or is_kw_arg or seen_named:
                  fail("Var args may not appear after named or var args", node)
                  break
              is_var_arg = True
          elif kind == ARG_NAMED or kind == ARG_NAMED_OPT:
              seen_named = True
              if is_kw_arg:
                  fail("A **kwargs argument must be the last argument", node)
                  break
          elif kind == ARG_STAR2:
              if is_kw_arg:
                  fail("You may only have one **kwargs argument", node)
                  break
              is_kw_arg = True
  
  
  def check_arg_names(names: Sequence[Optional[str]], nodes: List[T], fail: Callable[[str, T], None],
                      description: str = 'function definition') -> None:
      seen_names = set()  # type: Set[Optional[str]]
      for name, node in zip(names, nodes):
          if name is not None and name in seen_names:
              fail("Duplicate argument '{}' in {}".format(name, description), node)
              break
          seen_names.add(name)
  
  
  def is_class_var(expr: NameExpr) -> bool:
      """Return whether the expression is ClassVar[...]"""
      if isinstance(expr.node, Var):
          return expr.node.is_classvar
      return False
  
  
  def is_final_node(node: Optional[SymbolNode]) -> bool:
      """Check whether `node` corresponds to a final attribute."""
      return isinstance(node, (Var, FuncDef, OverloadedFuncDef, Decorator)) and node.is_final
  
  
  def local_definitions(names: SymbolTable,
                        name_prefix: str,
                        info: Optional[TypeInfo] = None) -> Iterator[Definition]:
      """Iterate over local definitions (not imported) in a symbol table.
  
      Recursively iterate over class members and nested classes.
      """
      # TODO: What should the name be? Or maybe remove it?
      for name, symnode in names.items():
          shortname = name
          if '-redef' in name:
              # Restore original name from mangled name of multiply defined function
              shortname = name.split('-redef')[0]
          fullname = name_prefix + '.' + shortname
          node = symnode.node
          if node and node.fullname == fullname:
              yield fullname, symnode, info
              if isinstance(node, TypeInfo):
                  yield from local_definitions(node.names, fullname, node)
  