text: from typing import Dict, List
  from typing_extensions import Final
  
  from mypy.nodes import (
      Block, AssignmentStmt, NameExpr, MypyFile, FuncDef, Lvalue, ListExpr, TupleExpr,
      WhileStmt, ForStmt, BreakStmt, ContinueStmt, TryStmt, WithStmt, StarExpr, ImportFrom,
      MemberExpr, IndexExpr, Import, ClassDef
  )
  from mypy.traverser import TraverserVisitor
  
  # Scope kinds
  FILE = 0  # type: Final
  FUNCTION = 1  # type: Final
  CLASS = 2  # type: Final
  
  
  class VariableRenameVisitor(TraverserVisitor):
      """Rename variables to allow redefinition of variables.
  
      For example, consider this code:
  
        x = 0
        f(x)
  
        x = "a"
        g(x)
  
      It will be transformed like this:
  
        x' = 0
        f(x')
  
        x = "a"
        g(x)
  
      There will be two independent variables (x' and x) that will have separate
      inferred types. The publicly exposed variant will get the non-suffixed name.
      This is the last definition at module top level and the first definition
      (argument) within a function.
  
      Renaming only happens for assignments within the same block. Renaming is
      performed before semantic analysis, immediately after parsing.
  
      The implementation performs a rudimentary static analysis. The analysis is
      overly conservative to keep things simple.
      """
  
      def __init__(self) -> None:
          # Counter for labeling new blocks
          self.block_id = 0
          # Number of surrounding try statements that disallow variable redefinition
          self.disallow_redef_depth = 0
          # Number of surrounding loop statements
          self.loop_depth = 0
          # Map block id to loop depth.
          self.block_loop_depth = {}  # type: Dict[int, int]
          # Stack of block ids being processed.
          self.blocks = []  # type: List[int]
          # List of scopes; each scope maps short (unqualified) name to block id.
          self.var_blocks = []  # type: List[Dict[str, int]]
  
          # References to variables that we may need to rename. List of
          # scopes; each scope is a mapping from name to list of collections
          # of names that refer to the same logical variable.
          self.refs = []  # type: List[Dict[str, List[List[NameExpr]]]]
          # Number of reads of the most recent definition of a variable (per scope)
          self.num_reads = []  # type: List[Dict[str, int]]
          # Kinds of nested scopes (FILE, FUNCTION or CLASS)
          self.scope_kinds = []  # type: List[int]
  
      def visit_mypy_file(self, file_node: MypyFile) -> None:
          """Rename variables within a file.
  
          This is the main entry point to this class.
          """
          self.clear()
          self.enter_scope(FILE)
          self.enter_block()
  
          for d in file_node.defs:
              d.accept(self)
  
          self.leave_block()
          self.leave_scope()
  
      def visit_func_def(self, fdef: FuncDef) -> None:
          # Conservatively do not allow variable defined before a function to
          # be redefined later, since function could refer to either definition.
          self.reject_redefinition_of_vars_in_scope()
  
          self.enter_scope(FUNCTION)
          self.enter_block()
  
          for arg in fdef.arguments:
              name = arg.variable.name
              # 'self' can't be redefined since it's special as it allows definition of
              # attributes. 'cls' can't be used to define attributes so we can ignore it.
              can_be_redefined = name != 'self'  # TODO: Proper check
              self.record_assignment(arg.variable.name, can_be_redefined)
              self.handle_arg(name)
  
          for stmt in fdef.body.body:
              stmt.accept(self)
  
          self.leave_block()
          self.leave_scope()
  
      def visit_class_def(self, cdef: ClassDef) -> None:
          self.reject_redefinition_of_vars_in_scope()
          self.enter_scope(CLASS)
          super().visit_class_def(cdef)
          self.leave_scope()
  
      def visit_block(self, block: Block) -> None:
          self.enter_block()
          super().visit_block(block)
          self.leave_block()
  
      def visit_while_stmt(self, stmt: WhileStmt) -> None:
          self.enter_loop()
          super().visit_while_stmt(stmt)
          self.leave_loop()
  
      def visit_for_stmt(self, stmt: ForStmt) -> None:
          stmt.expr.accept(self)
          self.analyze_lvalue(stmt.index, True)
          # Also analyze as non-lvalue so that every for loop index variable is assumed to be read.
          stmt.index.accept(self)
          self.enter_loop()
          stmt.body.accept(self)
          self.leave_loop()
          if stmt.else_body:
              stmt.else_body.accept(self)
  
      def visit_break_stmt(self, stmt: BreakStmt) -> None:
          self.reject_redefinition_of_vars_in_loop()
  
      def visit_continue_stmt(self, stmt: ContinueStmt) -> None:
          self.reject_redefinition_of_vars_in_loop()
  
      def visit_try_stmt(self, stmt: TryStmt) -> None:
          # Variables defined by a try statement get special treatment in the
          # type checker which allows them to be always redefined, so no need to
          # do renaming here.
          self.enter_try()
          super().visit_try_stmt(stmt)
          self.leave_try()
  
      def visit_with_stmt(self, stmt: WithStmt) -> None:
          for expr in stmt.expr:
              expr.accept(self)
          for target in stmt.target:
              if target is not None:
                  self.analyze_lvalue(target)
          # We allow redefinitions in the body of a with statement for
          # convenience.  This is unsafe since with statements can affect control
          # flow by catching exceptions, but this is rare except for
          # assertRaises() and other similar functions, where the exception is
          # raised by the last statement in the body, which usually isn't a
          # problem.
          stmt.body.accept(self)
  
      def visit_import(self, imp: Import) -> None:
          for id, as_id in imp.ids:
              self.record_assignment(as_id or id, False)
  
      def visit_import_from(self, imp: ImportFrom) -> None:
          for id, as_id in imp.names:
              self.record_assignment(as_id or id, False)
  
      def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
          s.rvalue.accept(self)
          for lvalue in s.lvalues:
              self.analyze_lvalue(lvalue)
  
      def analyze_lvalue(self, lvalue: Lvalue, is_nested: bool = False) -> None:
          """Process assignment; in particular, keep track of (re)defined names.
  
          Args:
              is_nested: True for non-outermost Lvalue in a multiple assignment such as
                  "x, y = ..."
          """
          if isinstance(lvalue, NameExpr):
              name = lvalue.name
              is_new = self.record_assignment(name, True)
              if is_new:
                  self.handle_def(lvalue)
              else:
                  self.handle_refine(lvalue)
              if is_nested:
                  # This allows these to be redefined freely even if never read. Multiple
                  # assignment like "x, _ _ = y" defines dummy variables that are never read.
                  self.handle_ref(lvalue)
          elif isinstance(lvalue, (ListExpr, TupleExpr)):
              for item in lvalue.items:
                  self.analyze_lvalue(item, is_nested=True)
          elif isinstance(lvalue, MemberExpr):
              lvalue.expr.accept(self)
          elif isinstance(lvalue, IndexExpr):
              lvalue.base.accept(self)
              lvalue.index.accept(self)
          elif isinstance(lvalue, StarExpr):
              # Propagate is_nested since in a typical use case like "x, *rest = ..." 'rest' may
              # be freely reused.
              self.analyze_lvalue(lvalue.expr, is_nested=is_nested)
  
      def visit_name_expr(self, expr: NameExpr) -> None:
          self.handle_ref(expr)
  
      # Helpers for renaming references
  
      def handle_arg(self, name: str) -> None:
          """Store function argument."""
          self.refs[-1][name] = [[]]
          self.num_reads[-1][name] = 0
  
      def handle_def(self, expr: NameExpr) -> None:
          """Store new name definition."""
          name = expr.name
          names = self.refs[-1].setdefault(name, [])
          names.append([expr])
          self.num_reads[-1][name] = 0
  
      def handle_refine(self, expr: NameExpr) -> None:
          """Store assignment to an existing name (that replaces previous value, if any)."""
          name = expr.name
          if name in self.refs[-1]:
              names = self.refs[-1][name]
              if not names:
                  names.append([])
              names[-1].append(expr)
  
      def handle_ref(self, expr: NameExpr) -> None:
          """Store reference to defined name."""
          name = expr.name
          if name in self.refs[-1]:
              names = self.refs[-1][name]
              if not names:
                  names.append([])
              names[-1].append(expr)
          num_reads = self.num_reads[-1]
          num_reads[name] = num_reads.get(name, 0) + 1
  
      def flush_refs(self) -> None:
          """Rename all references within the current scope.
  
          This will be called at the end of a scope.
          """
          is_func = self.scope_kinds[-1] == FUNCTION
          for name, refs in self.refs[-1].items():
              if len(refs) == 1:
                  # Only one definition -- no renaming needed.
                  continue
              if is_func:
                  # In a function, don't rename the first definition, as it
                  # may be an argument that must preserve the name.
                  to_rename = refs[1:]
              else:
                  # At module top level, don't rename the final definition,
                  # as it will be publicly visible outside the module.
                  to_rename = refs[:-1]
              for i, item in enumerate(to_rename):
                  self.rename_refs(item, i)
          self.refs.pop()
  
      def rename_refs(self, names: List[NameExpr], index: int) -> None:
          name = names[0].name
          new_name = name + "'" * (index + 1)
          for expr in names:
              expr.name = new_name
  
      # Helpers for determining which assignments define new variables
  
      def clear(self) -> None:
          self.blocks = []
          self.var_blocks = []
  
      def enter_block(self) -> None:
          self.block_id += 1
          self.blocks.append(self.block_id)
          self.block_loop_depth[self.block_id] = self.loop_depth
  
      def leave_block(self) -> None:
          self.blocks.pop()
  
      def enter_try(self) -> None:
          self.disallow_redef_depth += 1
  
      def leave_try(self) -> None:
          self.disallow_redef_depth -= 1
  
      def enter_loop(self) -> None:
          self.loop_depth += 1
  
      def leave_loop(self) -> None:
          self.loop_depth -= 1
  
      def current_block(self) -> int:
          return self.blocks[-1]
  
      def enter_scope(self, kind: int) -> None:
          self.var_blocks.append({})
          self.refs.append({})
          self.num_reads.append({})
          self.scope_kinds.append(kind)
  
      def leave_scope(self) -> None:
          self.flush_refs()
          self.var_blocks.pop()
          self.num_reads.pop()
          self.scope_kinds.pop()
  
      def is_nested(self) -> int:
          return len(self.var_blocks) > 1
  
      def reject_redefinition_of_vars_in_scope(self) -> None:
          """Make it impossible to redefine defined variables in the current scope.
  
          This is used if we encounter a function definition that
          can make it ambiguous which definition is live. Example:
  
            x = 0
  
            def f() -> int:
                return x
  
            x = ''  # Error -- cannot redefine x across function definition
          """
          var_blocks = self.var_blocks[-1]
          for key in var_blocks:
              var_blocks[key] = -1
  
      def reject_redefinition_of_vars_in_loop(self) -> None:
          """Reject redefinition of variables in the innermost loop.
  
          If there is an early exit from a loop, there may be ambiguity about which
          value may escape the loop. Example where this matters:
  
            while f():
                x = 0
                if g():
                    break
                x = ''  # Error -- not a redefinition
            reveal_type(x)  # int
  
          This method ensures that the second assignment to 'x' doesn't introduce a new
          variable.
          """
          var_blocks = self.var_blocks[-1]
          for key, block in var_blocks.items():
              if self.block_loop_depth.get(block) == self.loop_depth:
                  var_blocks[key] = -1
  
      def record_assignment(self, name: str, can_be_redefined: bool) -> bool:
          """Record assignment to given name and return True if it defines a new variable.
  
          Args:
              can_be_redefined: If True, allows assignment in the same block to redefine
                  this name (if this is a new definition)
          """
          if self.num_reads[-1].get(name, -1) == 0:
              # Only set, not read, so no reason to redefine
              return False
          if self.disallow_redef_depth > 0:
              # Can't redefine within try/with a block.
              can_be_redefined = False
          block = self.current_block()
          var_blocks = self.var_blocks[-1]
          if name not in var_blocks:
              # New definition in this scope.
              if can_be_redefined:
                  # Store the block where this was defined to allow redefinition in
                  # the same block only.
                  var_blocks[name] = block
              else:
                  # This doesn't support arbitrary redefinition.
                  var_blocks[name] = -1
              return True
          elif var_blocks[name] == block:
              # Redefinition -- defines a new variable with the same name.
              return True
          else:
              # Assigns to an existing variable.
              return False
  