django/django/utils/module_loading.py

from __future__ import absolute_import  # Avoid importing `importlib` from this package.

import copy
import imp
from importlib import import_module
import os
import sys

from django.core.exceptions import ImproperlyConfigured
from django.utils import six


def import_by_path(dotted_path, error_prefix=''):
    """
    Import a dotted module path and return the attribute/class designated by the
    last name in the path. Raise ImproperlyConfigured if something goes wrong.
    """
    try:
        module_path, class_name = dotted_path.rsplit('.', 1)
    except ValueError:
        raise ImproperlyConfigured("%s%s doesn't look like a module path" % (
            error_prefix, dotted_path))
    try:
        module = import_module(module_path)
    except ImportError as e:
        msg = '%sError importing module %s: "%s"' % (
            error_prefix, module_path, e)
        six.reraise(ImproperlyConfigured, ImproperlyConfigured(msg),
                    sys.exc_info()[2])
    try:
        attr = getattr(module, class_name)
    except AttributeError:
        raise ImproperlyConfigured('%sModule "%s" does not define a "%s" attribute/class' % (
            error_prefix, module_path, class_name))
    return attr


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.conf import settings

    register_to = kwargs.get('register_to')
    for app in settings.INSTALLED_APPS:
        mod = import_module(app)
        # Attempt to import the app's module.
        try:
            if register_to:
                before_import_registry = copy.copy(register_to._registry)

            for module_to_search in args:
                import_module('%s.%s' % (app, module_to_search))
        except:
            # Reset the model 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 an admin module, we can ignore the error
            # attempting to import it, otherwise we want it to bubble up.
            if module_has_submodule(mod, module_to_search):
                raise


def module_has_submodule(package, module_name):
    """See if 'module' is in 'package'."""
    name = ".".join([package.__name__, module_name])
    try:
        # None indicates a cached miss; see mark_miss() in Python/import.c.
        return sys.modules[name] is not None
    except KeyError:
        pass
    try:
        package_path = package.__path__   # No __path__, then not a package.
    except AttributeError:
        # Since the remainder of this function assumes that we're dealing with
        # a package (module with a __path__), so if it's not, then bail here.
        return False
    for finder in sys.meta_path:
        if finder.find_module(name, package_path):
            return True
    for entry in package_path:
        try:
            # Try the cached finder.
            finder = sys.path_importer_cache[entry]
            if finder is None:
                # Implicit import machinery should be used.
                try:
                    file_, _, _ = imp.find_module(module_name, [entry])
                    if file_:
                        file_.close()
                    return True
                except ImportError:
                    continue
            # Else see if the finder knows of a loader.
            elif finder.find_module(name):
                return True
            else:
                continue
        except KeyError:
            # No cached finder, so try and make one.
            for hook in sys.path_hooks:
                try:
                    finder = hook(entry)
                    # XXX Could cache in sys.path_importer_cache
                    if finder.find_module(name):
                        return True
                    else:
                        # Once a finder is found, stop the search.
                        break
                except ImportError:
                    # Continue the search for a finder.
                    continue
            else:
                # No finder found.
                # Try the implicit import machinery if searching a directory.
                if os.path.isdir(entry):
                    try:
                        file_, _, _ = imp.find_module(module_name, [entry])
                        if file_:
                            file_.close()
                        return True
                    except ImportError:
                        pass
                # XXX Could insert None or NullImporter
    else:
        # Exhausted the search, so the module cannot be found.
        return False