             check_version_list.append(base_list_entry)

        for check_version in check_version_list:
            is_third_party = base != 'stdlib'
            yield PathInfo(str(base_path.joinpath(check_version)), is_third_party)


_version_cache: Dict[Tuple[int, int], Mapping[str, PathInfo]] = {}


def _cache_stub_file_map(version_info):
    """
    Returns a map of an importable name in Python to a stub file.
    """
    # TODO this caches the stub files indefinitely, maybe use a time cache
    # for that?
    version = version_info[:2]
    try:
        return _version_cache[version]
    except KeyError:
        pass

    _version_cache[version] = file_set = \
        _merge_create_stub_map(_get_typeshed_directories(version_info))
    return file_set


def import_module_decorator(func):
    @wraps(func)
    def wrapper(inference_state, import_names, parent_module_value, sys_path, prefer_stubs):
        python_value_set = inference_state.module_cache.get(import_names)
        if python_value_set is None:
            if parent_module_value is not None and parent_module_value.is_stub():
                parent_module_values = parent_module_value.non_stub_value_set
            else:
                parent_module_values = [parent_module_value]
            if import_names == ('os', 'path'):
                # This is a huge exception, we follow a nested import
                # ``os.path``, because it's a very important one in Python
                # that is being achieved by messing with ``sys.modules`` in
                # ``os``.
                python_value_set = ValueSet.from_sets(
                    func(inference_state, (n,), None, sys_path,)
                    for n in ['posixpath', 'ntpath', 'macpath', 'os2emxpath']
                )
            else:
                python_value_set = ValueSet.from_sets(
                    func(inference_state, import_names, p, sys_path,)
                    for p in parent_module_values
                )
            inference_state.module_cache.add(import_names, python_value_set)

        if not prefer_stubs or import_names[0] in settings.auto_import_modules:
            return python_value_set

        stub = try_to_load_stub_cached(inference_state, import_names, python_value_set,
                                       parent_module_value, sys_path)
        if stub is not None:
            return ValueSet([stub])
        return python_value_set

    return wrapper


def try_to_load_stub_cached(inference_state, import_names, *args, **kwargs):
    if import_names is None:
        return None

    try:
        return inference_state.stub_module_cache[import_names]
    except KeyError:
        pass

    # TODO is this needed? where are the exceptions coming from that make this
    # necessary? Just remove this line.
    inference_state.stub_module_cache[import_names] = None
    inference_state.stub_module_cache[import_names] = result = \
        _try_to_load_stub(inference_state, import_names, *args, **kwargs)
    return result


def _try_to_load_stub(inference_state, import_names, python_value_set,
                      parent_module_value, sys_path):
    """
    Trying to load a stub for a set of import_names.

    This is modelled to work like "PEP 561 -- Distributing and Packaging Type
    Information", see https://www.python.org/dev/peps/pep-0561.
    """
    if parent_module_value is None and len(import_names) > 1:
        try:
            parent_module_value = try_to_load_stub_cached(
                inference_state, import_names[:-1], NO_VALUES,
                parent_module_value=None, sys_path=sys_path)
        except KeyError:
            pass

    # 1. Try to load foo-stubs folders on path for import name foo.
    if len(import_names) == 1:
        # foo-stubs
        for p in sys_path:
            init = os.path.join(p, *import_names) + '-stubs' + os.path.sep + '__init__.pyi'
            m = _try_to_load_stub_from_file(
                inference_state,
                python_value_set,
                file_io=FileIO(init),
                import_names=import_names,
            )
            if m is not None:
                return m
        if import_names[0] == 'django' and python_value_set:
            return _try_to_load_stub_from_file(
                inference_state,
                python_value_set,
                file_io=FileIO(str(DJANGO_INIT_PATH)),
                import_names=import_names,
            )

    # 2. Try to load pyi files next to py files.
    for c in python_value_set:
        try:
            method = c.py__file__
        except AttributeError:
            pass
        else:
            file_path = method()
            file_paths = []
            if c.is_namespace():
                file_paths = [os.path.join(p, '__init__.pyi') for p in c.py__path__()]
            elif file_path is not None and file_path.suffix == '.py':
                file_paths = [str(file_path) + 'i']

            for file_path in file_paths:
                m = _try_to_load_stub_from_file(
                    inference_state,
                    python_value_set,
                    # The file path should end with .pyi
                    file_io=FileIO(file_path),
                    import_names=import_names,
                )
                if m is not None:
                    return m

    # 3. Try to load typeshed
    m = _load_from_typeshed(inference_state, python_value_set, parent_module_value, import_names)
    if m is not None:
        return m

    # 4. Try to load pyi file somewhere if python_value_set was not defined.
    if not python_value_set:
        if parent_module_value is not None:
            check_path = parent_module_value.py__path__() or []
            # In case import_names
            names_for_path = (import_names[-1],)
        else:
            check_path = sys_path
            names_for_path = import_names

        for p in check_path:
            m = _try_to_load_stub_from_file(
                inference_state,
                python_value_set,
                file_io=FileIO(os.path.join(p, *names_for_path) + '.pyi'),
                import_names=import_names,
            )
            if m is not None:
                return m

    # If no stub is found, that's fine, the calling function has to deal with
    # it.
    return None


def _load_from_typeshed(inference_state, python_value_set, parent_module_value, import_names):
    import_name = import_names[-1]
    map_ = None
    if len(import_names) == 1:
        map_ = _cache_stub_file_map(inference_state.grammar.version_info)
        import_name = _IMPORT_MAP.get(import_name, import_name)
    elif isinstance(parent_module_value, ModuleValue):
        if not parent_module_value.is_package():
            # Only if it's a package (= a folder) something can be
            # imported.
            return None
        paths = parent_module_value.py__path__()
        # Once the initial package has been loaded, the sub packages will
        # always be loaded, regardless if they are there or not. This makes
        # sense, IMO, because stubs take preference, even if the original
        # library doesn't provide a module (it could be dynamic). ~dave
        map_ = _merge_create_stub_map([PathInfo(p, is_third_party=False) for p in paths])

    if map_ is not None:
        path_info = map_.get(import_name)
        if path_info is not None and (not path_info.is_third_party or python_value_set):
            return _try_to_load_stub_from_file(
                inference_state,
                python_value_set,
                file_io=FileIO(path_info.path),
                import_names=import_names,
            )


def _try_to_load_stub_from_file(inference_state, python_value_set, file_io, import_names):
    try:
        stub_module_node = parse_stub_module(inference_state, file_io)
    except OSError:
        # The file that you're looking for doesn't exist (anymore).
        return None
    else:
        return create_stub_module(
            inference_state, inference_state.latest_grammar, python_value_set,
            stub_module_node, file_io, import_names
        )


def parse_stub_module(inference_state, file_io):
    return inference_state.parse(
        file_io=file_io,
        cache=True,
        diff_cache=settings.fast_parser,
        cache_path=settings.cache_directory,
        use_latest_grammar=True
    )


def create_stub_module(inference_state, grammar, python_value_set,
                       stub_module_node, file_io, import_names):
    if import_names == ('typing',):
        module_cls = TypingModuleWrapper
    else:
        module_cls = StubModuleValue
    file_name = os.path.basename(file_io.path)
    stub_module_value = module_cls(
        python_value_set, inference_state, stub_module_node,
        file_io=file_io,
        string_names=import_names,
        # The code was loaded with latest_grammar, so use
        # that.
        code_lines=get_cached_code_lines(grammar, file_io.path),
        is_package=file_name == '__init__.pyi',
    )
    return stub_module_value
PK