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# 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)
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