/brz/remove-bazaar

# Copyright (C) 2006 by 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""Functionality to create lazy evaluation objects.

This includes waiting to import a module until it is actually used.

"""

import sys

class ScopeReplacer(object):

    """A lazy object that will replace itself in the appropriate scope.

    This object sits, ready to create the real object the first time it is

    needed.

    """

    __slots__ = ('_scope', '_factory', '_name')

    def __init__(self, scope, factory, name):

        """Create a temporary object in the specified scope.

        Once used, a real object will be placed in the scope.

        :param scope: The scope the object should appear in

        :param factory: A callable that will create the real object.

            It will be passed (self, scope, name)

        :param name: The variable name in the given scope.

        """

        self._scope = scope

        self._factory = factory

        self._name = name

        scope[name] = self

    def _replace(self):

        """Actually replace self with other in the given scope"""

        factory = object.__getattribute__(self, '_factory')

        scope = object.__getattribute__(self, '_scope')

        name = object.__getattribute__(self, '_name')

        obj = factory(self, scope, name)

        scope[name] = obj

        return obj

    def _cleanup(self):

        """Stop holding on to all the extra stuff"""

        del self._factory

        del self._scope

        del self._name

    def __getattribute__(self, attr):

        obj = object.__getattribute__(self, '_replace')()

        object.__getattribute__(self, '_cleanup')()

        return getattr(obj, attr)

    def __call__(self, *args, **kwargs):

        obj = object.__getattribute__(self, '_replace')()

        object.__getattribute__(self, '_cleanup')()

        return obj(*args, **kwargs)