Django/venv/lib/python3.7/site-packages/django/utils/module_loading.py

import copy
import os
from importlib import import_module
from importlib.util import find_spec as importlib_find


def import_string(dotted_path):
    """
    Import a dotted module path and return the attribute/class designated by the
    last name in the path. Raise ImportError if the import failed.
    """
    try:
        module_path, class_name = dotted_path.rsplit('.', 1)
    except ValueError as err:
        raise ImportError("%s doesn't look like a module path" % dotted_path) from err

    module = import_module(module_path)

    try:
        return getattr(module, class_name)
    except AttributeError as err:
        raise ImportError('Module "%s" does not define a "%s" attribute/class' % (
            module_path, class_name)
        ) from err


def autodiscover_modules(*args, **kwargs):
    """
    Auto-discover INSTALLED_APPS modules and fail silently when
    not present. This forces an import on them to register any admin bits they
    may want.

    You may provide a register_to keyword parameter as a way to access a
    registry. This register_to object must have a _registry instance variable
    to access it.
    """
    from django.apps import apps

    register_to = kwargs.get('register_to')
    for app_config in apps.get_app_configs():
        for module_to_search in args:
            # Attempt to import the app's module.
            try:
                if register_to:
                    before_import_registry = copy.copy(register_to._registry)

                import_module('%s.%s' % (app_config.name, module_to_search))
            except Exception:
                # Reset the registry to the state before the last import
                # as this import will have to reoccur on the next request and
                # this could raise NotRegistered and AlreadyRegistered
                # exceptions (see #8245).
                if register_to:
                    register_to._registry = before_import_registry

                # Decide whether to bubble up this error. If the app just
                # doesn't have the module in question, we can ignore the error
                # attempting to import it, otherwise we want it to bubble up.
                if module_has_submodule(app_config.module, module_to_search):
                    raise


def module_has_submodule(package, module_name):
    """See if 'module' is in 'package'."""
    try:
        package_name = package.__name__
        package_path = package.__path__
    except AttributeError:
        # package isn't a package.
        return False

    full_module_name = package_name + '.' + module_name
    try:
        return importlib_find(full_module_name, package_path) is not None
    except (ImportError, AttributeError):
        # When module_name is an invalid dotted path, Python raises ImportError
        # (or ModuleNotFoundError in Python 3.6+). AttributeError may be raised
        # if the penultimate part of the path is not a package.
        # (https://bugs.python.org/issue30436)
        return False


def module_dir(module):
    """
    Find the name of the directory that contains a module, if possible.

    Raise ValueError otherwise, e.g. for namespace packages that are split
    over several directories.
    """
    # Convert to list because _NamespacePath does not support indexing on 3.3.
    paths = list(getattr(module, '__path__', []))
    if len(paths) == 1:
        return paths[0]
    else:
        filename = getattr(module, '__file__', None)
        if filename is not None:
            return os.path.dirname(filename)
    raise ValueError("Cannot determine directory containing %s" % module)