loading.py 文件源码

def _find_installed_apps_entry(module_label):
    """
    Given a module label, finds the best matching INSTALLED_APPS entry.

    This is made trickier by the fact that we don't know what part of the
    module_label is part of the INSTALLED_APPS entry. So we try all possible
    combinations, trying the longer versions first. E.g. for
    'dashboard.catalogue.forms', 'dashboard.catalogue' is attempted before
    'dashboard'
    """
    modules = module_label.split('.')
    # if module_label is 'dashboard.catalogue.forms.widgets', combinations
    # will be ['dashboard.catalogue.forms', 'dashboard.catalogue', 'dashboard']
    combinations = [
        '.'.join(modules[:-count]) for count in range(1, len(modules))]
    for app_name in combinations:
        entry = _get_installed_apps_entry(app_name)
        if entry:
            return entry, app_name
    raise AppNotFoundError(
        "Couldn't find an app to import %s from" % module_label)