~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2010 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

"""General Python convenience functions."""

from __future__ import absolute_import

import sys

def get_named_object(module_name, member_name=None):

    """Get the Python object named by a given module and member name.

    This is usually much more convenient than dealing with ``__import__``

    directly::

        >>> doc = get_named_object('bzrlib.pyutils', 'get_named_object.__doc__')

        >>> doc.splitlines()[0]

        'Get the Python object named by a given module and member name.'

    :param module_name: a module name, as would be found in sys.modules if

        the module is already imported.  It may contain dots.  e.g. 'sys' or

        'os.path'.

    :param member_name: (optional) a name of an attribute in that module to

        return.  It may contain dots.  e.g. 'MyClass.some_method'.  If not

        given, the named module will be returned instead.

    :raises: ImportError or AttributeError.

    """

    # We may have just a module name, or a module name and a member name,

    # and either may contain dots.  __import__'s return value is a bit

    # unintuitive, so we need to take care to always return the object

    # specified by the full combination of module name + member name.

    if member_name:

        # Give __import__ a from_list.  It will return the last module in

        # the dotted module name.

        attr_chain = member_name.split('.')

        from_list = attr_chain[:1]

        obj = __import__(module_name, {}, {}, from_list)

        for attr in attr_chain:

            obj = getattr(obj, attr)

    else:

        # We're just importing a module, no attributes, so we have no

        # from_list.  __import__ will return the first module in the dotted

        # module name, so we look up the module from sys.modules.

        __import__(module_name, globals(), locals(), [])

        obj = sys.modules[module_name]

    return obj

def calc_parent_name(module_name, member_name=None):

    """Determine the 'parent' of a given dotted module name and (optional)

    member name.

    The idea is that ``getattr(parent_obj, final_attr)`` will equal

    get_named_object(module_name, member_name).

    :return: (module_name, member_name, final_attr) tuple.

    """

# +SKIP is not recognized by python2.4

# Typical use is::

# 

#     >>> parent_mod, parent_member, final_attr = calc_parent_name(

#     ...     module_name, member_name) # doctest: +SKIP

#     >>> parent_obj = get_named_object(parent_mod, parent_member)

#     ... # doctest: +SKIP

    if member_name is not None:

        split_name = member_name.rsplit('.', 1)

        if len(split_name) == 1:

            return (module_name, None, member_name)

        else:

            return (module_name, split_name[0], split_name[1])

    else:

        split_name = module_name.rsplit('.', 1)

        if len(split_name) == 1:

            raise AssertionError(

                'No parent object for top-level module %r' % (module_name,))

        else:

            return (split_name[0], None, split_name[1])