tempest/openstack/common/importutils.py

# Copyright 2011 OpenStack Foundation.
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""
Import related utilities and helper functions.
"""

import sys
import traceback


def import_class(import_str):
    """Returns a class from a string including module and class."""
    mod_str, _sep, class_str = import_str.rpartition('.')
    try:
        __import__(mod_str)
        return getattr(sys.modules[mod_str], class_str)
    except (ValueError, AttributeError):
        raise ImportError('Class %s cannot be found (%s)' %
                          (class_str,
                           traceback.format_exception(*sys.exc_info())))


def import_object(import_str, *args, **kwargs):
    """Import a class and return an instance of it."""
    return import_class(import_str)(*args, **kwargs)


def import_object_ns(name_space, import_str, *args, **kwargs):
    """Tries to import object from default namespace.

    Imports a class and return an instance of it, first by trying
    to find the class in a default namespace, then failing back to
    a full path if not found in the default namespace.
    """
    import_value = "%s.%s" % (name_space, import_str)
    try:
        return import_class(import_value)(*args, **kwargs)
    except ImportError:
        return import_class(import_str)(*args, **kwargs)


def import_module(import_str):
    """Import a module."""
    __import__(import_str)
    return sys.modules[import_str]


def try_import(import_str, default=None):
    """Try to import a module and if it fails return default."""
    try:
        return import_module(import_str)
    except ImportError:
        return default