text: """Utilities to support packages."""
  
  from collections import namedtuple
  from functools import singledispatch as simplegeneric
  import importlib
  import importlib.util
  import importlib.machinery
  import os
  import os.path
  import re
  import sys
  from types import ModuleType
  import warnings
  
  __all__ = [
      'get_importer', 'iter_importers', 'get_loader', 'find_loader',
      'walk_packages', 'iter_modules', 'get_data',
      'ImpImporter', 'ImpLoader', 'read_code', 'extend_path',
      'ModuleInfo',
  ]
  
  
  ModuleInfo = namedtuple('ModuleInfo', 'module_finder name ispkg')
  ModuleInfo.__doc__ = 'A namedtuple with minimal info about a module.'
  
  
  def _get_spec(finder, name):
      """Return the finder-specific module spec."""
      # Works with legacy finders.
      try:
          find_spec = finder.find_spec
      except AttributeError:
          loader = finder.find_module(name)
          if loader is None:
              return None
          return importlib.util.spec_from_loader(name, loader)
      else:
          return find_spec(name)
  
  
  def read_code(stream):
      # This helper is needed in order for the PEP 302 emulation to
      # correctly handle compiled files
      import marshal
  
      magic = stream.read(4)
      if magic != importlib.util.MAGIC_NUMBER:
          return None
  
      stream.read(12) # Skip rest of the header
      return marshal.load(stream)
  
  
  def walk_packages(path=None, prefix='', onerror=None):
      """Yields ModuleInfo for all modules recursively
      on path, or, if path is None, all accessible modules.
  
      'path' should be either None or a list of paths to look for
      modules in.
  
      'prefix' is a string to output on the front of every module name
      on output.
  
      Note that this function must import all *packages* (NOT all
      modules!) on the given path, in order to access the __path__
      attribute to find submodules.
  
      'onerror' is a function which gets called with one argument (the
      name of the package which was being imported) if any exception
      occurs while trying to import a package.  If no onerror function is
      supplied, ImportErrors are caught and ignored, while all other
      exceptions are propagated, terminating the search.
  
      Examples:
  
      # list all modules python can access
      walk_packages()
  
      # list all submodules of ctypes
      walk_packages(ctypes.__path__, ctypes.__name__+'.')
      """
  
      def seen(p, m={}):
          if p in m:
              return True
          m[p] = True
  
      for info in iter_modules(path, prefix):
          yield info
  
          if info.ispkg:
              try:
                  __import__(info.name)
              except ImportError:
                  if onerror is not None:
                      onerror(info.name)
              except Exception:
                  if onerror is not None:
                      onerror(info.name)
                  else:
                      raise
              else:
                  path = getattr(sys.modules[info.name], '__path__', None) or []
  
                  # don't traverse path items we've seen before
                  path = [p for p in path if not seen(p)]
  
                  yield from walk_packages(path, info.name+'.', onerror)
  
  
  def iter_modules(path=None, prefix=''):
      """Yields ModuleInfo for all submodules on path,
      or, if path is None, all top-level modules on sys.path.
  
      'path' should be either None or a list of paths to look for
      modules in.
  
      'prefix' is a string to output on the front of every module name
      on output.
      """
      if path is None:
          importers = iter_importers()
      elif isinstance(path, str):
          raise ValueError("path must be None or list of paths to look for "
                          "modules in")
      else:
          importers = map(get_importer, path)
  
      yielded = {}
      for i in importers:
          for name, ispkg in iter_importer_modules(i, prefix):
              if name not in yielded:
                  yielded[name] = 1
                  yield ModuleInfo(i, name, ispkg)
  
  
  @simplegeneric
  def iter_importer_modules(importer, prefix=''):
      if not hasattr(importer, 'iter_modules'):
          return []
      return importer.iter_modules(prefix)
  
  
  # Implement a file walker for the normal importlib path hook
  def _iter_file_finder_modules(importer, prefix=''):
      if importer.path is None or not os.path.isdir(importer.path):
          return
  
      yielded = {}
      import inspect
      try:
          filenames = os.listdir(importer.path)
      except OSError:
          # ignore unreadable directories like import does
          filenames = []
      filenames.sort()  # handle packages before same-named modules
  
      for fn in filenames:
          modname = inspect.getmodulename(fn)
          if modname=='__init__' or modname in yielded:
              continue
  
          path = os.path.join(importer.path, fn)
          ispkg = False
  
          if not modname and os.path.isdir(path) and '.' not in fn:
              modname = fn
              try:
                  dircontents = os.listdir(path)
              except OSError:
                  # ignore unreadable directories like import does
                  dircontents = []
              for fn in dircontents:
                  subname = inspect.getmodulename(fn)
                  if subname=='__init__':
                      ispkg = True
                      break
              else:
                  continue    # not a package
  
          if modname and '.' not in modname:
              yielded[modname] = 1
              yield prefix + modname, ispkg
  
  iter_importer_modules.register(
      importlib.machinery.FileFinder, _iter_file_finder_modules)
  
  
  def _import_imp():
      global imp
      with warnings.catch_warnings():
          warnings.simplefilter('ignore', DeprecationWarning)
          imp = importlib.import_module('imp')
  
  class ImpImporter:
      """PEP 302 Finder that wraps Python's "classic" import algorithm
  
      ImpImporter(dirname) produces a PEP 302 finder that searches that
      directory.  ImpImporter(None) produces a PEP 302 finder that searches
      the current sys.path, plus any modules that are frozen or built-in.
  
      Note that ImpImporter does not currently support being used by placement
      on sys.meta_path.
      """
  
      def __init__(self, path=None):
          global imp
          warnings.warn("This emulation is deprecated, use 'importlib' instead",
               DeprecationWarning)
          _import_imp()
          self.path = path
  
      def find_module(self, fullname, path=None):
          # Note: we ignore 'path' argument since it is only used via meta_path
          subname = fullname.split(".")[-1]
          if subname != fullname and self.path is None:
              return None
          if self.path is None:
              path = None
          else:
              path = [os.path.realpath(self.path)]
          try:
              file, filename, etc = imp.find_module(subname, path)
          except ImportError:
              return None
          return ImpLoader(fullname, file, filename, etc)
  
      def iter_modules(self, prefix=''):
          if self.path is None or not os.path.isdir(self.path):
              return
  
          yielded = {}
          import inspect
          try:
              filenames = os.listdir(self.path)
          except OSError:
              # ignore unreadable directories like import does
              filenames = []
          filenames.sort()  # handle packages before same-named modules
  
          for fn in filenames:
              modname = inspect.getmodulename(fn)
              if modname=='__init__' or modname in yielded:
                  continue
  
              path = os.path.join(self.path, fn)
              ispkg = False
  
              if not modname and os.path.isdir(path) and '.' not in fn:
                  modname = fn
                  try:
                      dircontents = os.listdir(path)
                  except OSError:
                      # ignore unreadable directories like import does
                      dircontents = []
                  for fn in dircontents:
                      subname = inspect.getmodulename(fn)
                      if subname=='__init__':
                          ispkg = True
                          break
                  else:
                      continue    # not a package
  
              if modname and '.' not in modname:
                  yielded[modname] = 1
                  yield prefix + modname, ispkg
  
  
  class ImpLoader:
      """PEP 302 Loader that wraps Python's "classic" import algorithm
      """
      code = source = None
  
      def __init__(self, fullname, file, filename, etc):
          warnings.warn("This emulation is deprecated, use 'importlib' instead",
                        DeprecationWarning)
          _import_imp()
          self.file = file
          self.filename = filename
          self.fullname = fullname
          self.etc = etc
  
      def load_module(self, fullname):
          self._reopen()
          try:
              mod = imp.load_module(fullname, self.file, self.filename, self.etc)
          finally:
              if self.file:
                  self.file.close()
          # Note: we don't set __loader__ because we want the module to look
          # normal; i.e. this is just a wrapper for standard import machinery
          return mod
  
      def get_data(self, pathname):
          with open(pathname, "rb") as file:
              return file.read()
  
      def _reopen(self):
          if self.file and self.file.closed:
              mod_type = self.etc[2]
              if mod_type==imp.PY_SOURCE:
                  self.file = open(self.filename, 'r')
              elif mod_type in (imp.PY_COMPILED, imp.C_EXTENSION):
                  self.file = open(self.filename, 'rb')
  
      def _fix_name(self, fullname):
          if fullname is None:
              fullname = self.fullname
          elif fullname != self.fullname:
              raise ImportError("Loader for module %s cannot handle "
                                "module %s" % (self.fullname, fullname))
          return fullname
  
      def is_package(self, fullname):
          fullname = self._fix_name(fullname)
          return self.etc[2]==imp.PKG_DIRECTORY
  
      def get_code(self, fullname=None):
          fullname = self._fix_name(fullname)
          if self.code is None:
              mod_type = self.etc[2]
              if mod_type==imp.PY_SOURCE:
                  source = self.get_source(fullname)
                  self.code = compile(source, self.filename, 'exec')
              elif mod_type==imp.PY_COMPILED:
                  self._reopen()
                  try:
                      self.code = read_code(self.file)
                  finally:
                      self.file.close()
              elif mod_type==imp.PKG_DIRECTORY:
                  self.code = self._get_delegate().get_code()
          return self.code
  
      def get_source(self, fullname=None):
          fullname = self._fix_name(fullname)
          if self.source is None:
              mod_type = self.etc[2]
              if mod_type==imp.PY_SOURCE:
                  self._reopen()
                  try:
                      self.source = self.file.read()
                  finally:
                      self.file.close()
              elif mod_type==imp.PY_COMPILED:
                  if os.path.exists(self.filename[:-1]):
                      with open(self.filename[:-1], 'r') as f:
                          self.source = f.read()
              elif mod_type==imp.PKG_DIRECTORY:
                  self.source = self._get_delegate().get_source()
          return self.source
  
      def _get_delegate(self):
          finder = ImpImporter(self.filename)
          spec = _get_spec(finder, '__init__')
          return spec.loader
  
      def get_filename(self, fullname=None):
          fullname = self._fix_name(fullname)
          mod_type = self.etc[2]
          if mod_type==imp.PKG_DIRECTORY:
              return self._get_delegate().get_filename()
          elif mod_type in (imp.PY_SOURCE, imp.PY_COMPILED, imp.C_EXTENSION):
              return self.filename
          return None
  
  
  try:
      import zipimport
      from zipimport import zipimporter
  
      def iter_zipimport_modules(importer, prefix=''):
          dirlist = sorted(zipimport._zip_directory_cache[importer.archive])
          _prefix = importer.prefix
          plen = len(_prefix)
          yielded = {}
          import inspect
          for fn in dirlist:
              if not fn.startswith(_prefix):
                  continue
  
              fn = fn[plen:].split(os.sep)
  
              if len(fn)==2 and fn[1].startswith('__init__.py'):
                  if fn[0] not in yielded:
                      yielded[fn[0]] = 1
                      yield prefix + fn[0], True
  
              if len(fn)!=1:
                  continue
  
              modname = inspect.getmodulename(fn[0])
              if modname=='__init__':
                  continue
  
              if modname and '.' not in modname and modname not in yielded:
                  yielded[modname] = 1
                  yield prefix + modname, False
  
      iter_importer_modules.register(zipimporter, iter_zipimport_modules)
  
  except ImportError:
      pass
  
  
  def get_importer(path_item):
      """Retrieve a finder for the given path item
  
      The returned finder is cached in sys.path_importer_cache
      if it was newly created by a path hook.
  
      The cache (or part of it) can be cleared manually if a
      rescan of sys.path_hooks is necessary.
      """
      path_item = os.fsdecode(path_item)
      try:
          importer = sys.path_importer_cache[path_item]
      except KeyError:
          for path_hook in sys.path_hooks:
              try:
                  importer = path_hook(path_item)
                  sys.path_importer_cache.setdefault(path_item, importer)
                  break
              except ImportError:
                  pass
          else:
              importer = None
      return importer
  
  
  def iter_importers(fullname=""):
      """Yield finders for the given module name
  
      If fullname contains a '.', the finders will be for the package
      containing fullname, otherwise they will be all registered top level
      finders (i.e. those on both sys.meta_path and sys.path_hooks).
  
      If the named module is in a package, that package is imported as a side
      effect of invoking this function.
  
      If no module name is specified, all top level finders are produced.
      """
      if fullname.startswith('.'):
          msg = "Relative module name {!r} not supported".format(fullname)
          raise ImportError(msg)
      if '.' in fullname:
          # Get the containing package's __path__
          pkg_name = fullname.rpartition(".")[0]
          pkg = importlib.import_module(pkg_name)
          path = getattr(pkg, '__path__', None)
          if path is None:
              return
      else:
          yield from sys.meta_path
          path = sys.path
      for item in path:
          yield get_importer(item)
  
  
  def get_loader(module_or_name):
      """Get a "loader" object for module_or_name
  
      Returns None if the module cannot be found or imported.
      If the named module is not already imported, its containing package
      (if any) is imported, in order to establish the package __path__.
      """
      if module_or_name in sys.modules:
          module_or_name = sys.modules[module_or_name]
          if module_or_name is None:
              return None
      if isinstance(module_or_name, ModuleType):
          module = module_or_name
          loader = getattr(module, '__loader__', None)
          if loader is not None:
              return loader
          if getattr(module, '__spec__', None) is None:
              return None
          fullname = module.__name__
      else:
          fullname = module_or_name
      return find_loader(fullname)
  
  
  def find_loader(fullname):
      """Find a "loader" object for fullname
  
      This is a backwards compatibility wrapper around
      importlib.util.find_spec that converts most failures to ImportError
      and only returns the loader rather than the full spec
      """
      if fullname.startswith('.'):
          msg = "Relative module name {!r} not supported".format(fullname)
          raise ImportError(msg)
      try:
          spec = importlib.util.find_spec(fullname)
      except (ImportError, AttributeError, TypeError, ValueError) as ex:
          # This hack fixes an impedance mismatch between pkgutil and
          # importlib, where the latter raises other errors for cases where
          # pkgutil previously raised ImportError
          msg = "Error while finding loader for {!r} ({}: {})"
          raise ImportError(msg.format(fullname, type(ex), ex)) from ex
      return spec.loader if spec is not None else None
  
  
  def extend_path(path, name):
      """Extend a package's path.
  
      Intended use is to place the following code in a package's __init__.py:
  
          from pkgutil import extend_path
          __path__ = extend_path(__path__, __name__)
  
      This will add to the package's __path__ all subdirectories of
      directories on sys.path named after the package.  This is useful
      if one wants to distribute different parts of a single logical
      package as multiple directories.
  
      It also looks for *.pkg files beginning where * matches the name
      argument.  This feature is similar to *.pth files (see site.py),
      except that it doesn't special-case lines starting with 'import'.
      A *.pkg file is trusted at face value: apart from checking for
      duplicates, all entries found in a *.pkg file are added to the
      path, regardless of whether they are exist the filesystem.  (This
      is a feature.)
  
      If the input path is not a list (as is the case for frozen
      packages) it is returned unchanged.  The input path is not
      modified; an extended copy is returned.  Items are only appended
      to the copy at the end.
  
      It is assumed that sys.path is a sequence.  Items of sys.path that
      are not (unicode or 8-bit) strings referring to existing
      directories are ignored.  Unicode items of sys.path that cause
      errors when used as filenames may cause this function to raise an
      exception (in line with os.path.isdir() behavior).
      """
  
      if not isinstance(path, list):
          # This could happen e.g. when this is called from inside a
          # frozen package.  Return the path unchanged in that case.
          return path
  
      sname_pkg = name + ".pkg"
  
      path = path[:] # Start with a copy of the existing path
  
      parent_package, _, final_name = name.rpartition('.')
      if parent_package:
          try:
              search_path = sys.modules[parent_package].__path__
          except (KeyError, AttributeError):
              # We can't do anything: find_loader() returns None when
              # passed a dotted name.
              return path
      else:
          search_path = sys.path
  
      for dir in search_path:
          if not isinstance(dir, str):
              continue
  
          finder = get_importer(dir)
          if finder is not None:
              portions = []
              if hasattr(finder, 'find_spec'):
                  spec = finder.find_spec(final_name)
                  if spec is not None:
                      portions = spec.submodule_search_locations or []
              # Is this finder PEP 420 compliant?
              elif hasattr(finder, 'find_loader'):
                  _, portions = finder.find_loader(final_name)
  
              for portion in portions:
                  # XXX This may still add duplicate entries to path on
                  # case-insensitive filesystems
                  if portion not in path:
                      path.append(portion)
  
          # XXX Is this the right thing for subpackages like zope.app?
          # It looks for a file named "zope.app.pkg"
          pkgfile = os.path.join(dir, sname_pkg)
          if os.path.isfile(pkgfile):
              try:
                  f = open(pkgfile)
              except OSError as msg:
                  sys.stderr.write("Can't open %s: %s\n" %
                                   (pkgfile, msg))
              else:
                  with f:
                      for line in f:
                          line = line.rstrip('\n')
                          if not line or line.startswith('#'):
                              continue
                          path.append(line) # Don't check for existence!
  
      return path
  
  
  def get_data(package, resource):
      """Get a resource from a package.
  
      This is a wrapper round the PEP 302 loader get_data API. The package
      argument should be the name of a package, in standard module format
      (foo.bar). The resource argument should be in the form of a relative
      filename, using '/' as the path separator. The parent directory name '..'
      is not allowed, and nor is a rooted name (starting with a '/').
  
      The function returns a binary string, which is the contents of the
      specified resource.
  
      For packages located in the filesystem, which have already been imported,
      this is the rough equivalent of
  
          d = os.path.dirname(sys.modules[package].__file__)
          data = open(os.path.join(d, resource), 'rb').read()
  
      If the package cannot be located or loaded, or it uses a PEP 302 loader
      which does not support get_data(), then None is returned.
      """
  
      spec = importlib.util.find_spec(package)
      if spec is None:
          return None
      loader = spec.loader
      if loader is None or not hasattr(loader, 'get_data'):
          return None
      # XXX needs test
      mod = (sys.modules.get(package) or
             importlib._bootstrap._load(spec))
      if mod is None or not hasattr(mod, '__file__'):
          return None
  
      # Modify the resource name to be compatible with the loader.get_data
      # signature - an os.path format "filename" starting with the dirname of
      # the package's __file__
      parts = resource.split('/')
      parts.insert(0, os.path.dirname(mod.__file__))
      resource_name = os.path.join(*parts)
      return loader.get_data(resource_name)
  
  
  _DOTTED_WORDS = r'(?!\d)(\w+)(\.(?!\d)(\w+))*'
  _NAME_PATTERN = re.compile(f'^(?P<pkg>{_DOTTED_WORDS})(?P<cln>:(?P<obj>{_DOTTED_WORDS})?)?$', re.U)
  del _DOTTED_WORDS
  
  def resolve_name(name):
      """
      Resolve a name to an object.
  
      It is expected that `name` will be a string in one of the following
      formats, where W is shorthand for a valid Python identifier and dot stands
      for a literal period in these pseudo-regexes:
  
      W(.W)*
      W(.W)*:(W(.W)*)?
  
      The first form is intended for backward compatibility only. It assumes that
      some part of the dotted name is a package, and the rest is an object
      somewhere within that package, possibly nested inside other objects.
      Because the place where the package stops and the object hierarchy starts
      can't be inferred by inspection, repeated attempts to import must be done
      with this form.
  
      In the second form, the caller makes the division point clear through the
      provision of a single colon: the dotted name to the left of the colon is a
      package to be imported, and the dotted name to the right is the object
      hierarchy within that package. Only one import is needed in this form. If
      it ends with the colon, then a module object is returned.
  
      The function will return an object (which might be a module), or raise one
      of the following exceptions:
  
      ValueError - if `name` isn't in a recognised format
      ImportError - if an import failed when it shouldn't have
      AttributeError - if a failure occurred when traversing the object hierarchy
                       within the imported package to get to the desired object.
      """
      m = _NAME_PATTERN.match(name)
      if not m:
          raise ValueError(f'invalid format: {name!r}')
      gd = m.groupdict()
      if gd.get('cln'):
          # there is a colon - a one-step import is all that's needed
          mod = importlib.import_module(gd['pkg'])
          parts = gd.get('obj')
          parts = parts.split('.') if parts else []
      else:
          # no colon - have to iterate to find the package boundary
          parts = name.split('.')
          modname = parts.pop(0)
          # first part *must* be a module/package.
          mod = importlib.import_module(modname)
          while parts:
              p = parts[0]
              s = f'{modname}.{p}'
              try:
                  mod = importlib.import_module(s)
                  parts.pop(0)
                  modname = s
              except ImportError:
                  break
      # if we reach this point, mod is the module, already imported, and
      # parts is the list of parts in the object hierarchy to be traversed, or
      # an empty list if just the module is wanted.
      result = mod
      for p in parts:
          result = getattr(result, p)
      return result
  