############################################################################## # # Copyright (c) 2004 Zope Corporation and Contributors. # All Rights Reserved. # # This software is subject to the provisions of the Zope Public License, # Version 2.0 (ZPL). A copy of the ZPL should accompany this distribution. # THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED # WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED # WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS # FOR A PARTICULAR PURPOSE. # ############################################################################## """Broken object support $Id$ """ import sys import persistent broken_cache = {} class Broken(object): """Broken object base class Broken objects are placeholders for objects that can no longer be created because their class has gone away. Broken objects don't really do much of anything, except hold their state. The Broken class is used as a base class for creating classes in leu of missing classes:: >>> Atall = type('Atall', (Broken, ), {'__module__': 'not.there'}) The only thing the class can be used for is to create new objects:: >>> Atall() <broken not.there.Atall instance> >>> Atall().__Broken_newargs__ () >>> Atall().__Broken_initargs__ () >>> Atall(1, 2).__Broken_newargs__ (1, 2) >>> Atall(1, 2).__Broken_initargs__ (1, 2) >>> a = Atall.__new__(Atall, 1, 2) >>> a <broken not.there.Atall instance> >>> a.__Broken_newargs__ (1, 2) >>> a.__Broken_initargs__ You can't modify broken objects:: >>> a.x = 1 Traceback (most recent call last): ... BrokenModified: Can't change broken objects But you can set their state:: >>> a.__setstate__({'x': 1, }) You can pickle broken objects:: >>> r = a.__reduce__() >>> len(r) 3 >>> r[0] is rebuild True >>> r[1] ('not.there', 'Atall', 1, 2) >>> r[2] {'x': 1} >>> import cPickle >>> a2 = cPickle.loads(cPickle.dumps(a, 1)) >>> a2 <broken not.there.Atall instance> >>> a2.__Broken_newargs__ (1, 2) >>> a2.__Broken_initargs__ >>> a2.__Broken_state__ {'x': 1} Cleanup:: >>> broken_cache.clear() """ __Broken_state__ = __Broken_initargs__ = None __name__ = 'bob XXX' def __new__(class_, *args): result = object.__new__(class_) result.__dict__['__Broken_newargs__'] = args return result def __init__(self, *args): self.__dict__['__Broken_initargs__'] = args def __reduce__(self): """We pickle broken objects in hope of being able to fix them later """ return (rebuild, ((self.__class__.__module__, self.__class__.__name__) + self.__Broken_newargs__), self.__Broken_state__, ) def __setstate__(self, state): self.__dict__['__Broken_state__'] = state def __repr__(self): return "<broken %s.%s instance>" % ( self.__class__.__module__, self.__class__.__name__) def __setattr__(self, name, value): raise BrokenModified("Can't change broken objects") def find_global(modulename, globalname, # These are *not* optimizations. Callers can override these. Broken=Broken, type=type, ): """Find a global object, returning a broken class if it can't be found. This function looks up global variable in modules:: >>> import sys >>> find_global('sys', 'path') is sys.path True If an object can't be found, a broken class is returned:: >>> broken = find_global('ZODB.not.there', 'atall') >>> issubclass(broken, Broken) True >>> broken.__module__ 'ZODB.not.there' >>> broken.__name__ 'atall' Broken classes are cached:: >>> find_global('ZODB.not.there', 'atall') is broken True If we "repair" a missing global:: >>> class ZODBnotthere: ... atall = [] >>> sys.modules['ZODB.not'] = ZODBnotthere >>> sys.modules['ZODB.not.there'] = ZODBnotthere we can then get the repaired value:: >>> find_global('ZODB.not.there', 'atall') is ZODBnotthere.atall True Of course, if we beak it again:: >>> del sys.modules['ZODB.not'] >>> del sys.modules['ZODB.not.there'] we get the broken value:: >>> find_global('ZODB.not.there', 'atall') is broken True Cleanup:: >>> broken_cache.clear() """ try: __import__(modulename) except ImportError: pass else: module = sys.modules[modulename] try: return getattr(module, globalname) except AttributeError: pass try: return broken_cache[(modulename, globalname)] except KeyError: pass class_ = type(globalname, (Broken, ), {'__module__': modulename}) broken_cache[(modulename, globalname)] = class_ return class_ def rebuild(modulename, globalname, *args): """Recreate a broken object, possibly recreating the missing class This functions unpickles broken objects:: >>> broken = rebuild('ZODB.notthere', 'atall', 1, 2) >>> broken <broken ZODB.notthere.atall instance> >>> broken.__Broken_newargs__ (1, 2) If we "repair" the brokenness:: >>> class notthere: # fake notthere module ... class atall(object): ... def __new__(self, *args): ... ob = object.__new__(self) ... ob.args = args ... return ob ... def __repr__(self): ... return 'atall %s %s' % self.args >>> sys.modules['ZODB.notthere'] = notthere >>> rebuild('ZODB.notthere', 'atall', 1, 2) atall 1 2 >>> del sys.modules['ZODB.notthere'] Cleanup:: >>> broken_cache.clear() """ class_ = find_global(modulename, globalname) return class_.__new__(class_, *args) class BrokenModified(TypeError): """Attempt to modify a broken object """ class PersistentBroken(Broken, persistent.Persistent): r"""Persistent broken objects Persistent broken objects are used for broken objects that are also persistent. In addition to having to track the original object data, they need to handle persistent meta data. Persistent broken classes are created from existing broken classes using the persistentBroken, function:: >>> Atall = type('Atall', (Broken, ), {'__module__': 'not.there'}) >>> PAtall = persistentBroken(Atall) (Note that we always get the *same* persistent broken class for a given broken class:: >>> persistentBroken(Atall) is PAtall True ) Persistent broken classes work a lot like broken classes:: >>> a = PAtall.__new__(PAtall, 1, 2) >>> a <persistent broken not.there.Atall instance None> >>> a.__Broken_newargs__ (1, 2) >>> a.__Broken_initargs__ >>> a.x = 1 Traceback (most recent call last): ... BrokenModified: Can't change broken objects Unlike regular broken objects, persistent broken objects keep track of persistence meta data: >>> a._p_oid = '\0\0\0\0****' >>> a <persistent broken not.there.Atall instance '\x00\x00\x00\x00****'> and persistent broken objects aren't directly picklable: >>> a.__reduce__() Traceback (most recent call last): ... BrokenModified: """ \ r"""<persistent broken not.there.Atall instance '\x00\x00\x00\x00****'> but you can get their state: >>> a.__setstate__({'y': 2}) >>> a.__getstate__() {'y': 2} Cleanup:: >>> broken_cache.clear() """ def __new__(class_, *args): result = persistent.Persistent.__new__(class_) result.__dict__['__Broken_newargs__'] = args return result def __reduce__(self, *args): raise BrokenModified(self) def __getstate__(self): return self.__Broken_state__ def __setattr__(self, name, value): if name.startswith('_p_'): persistent.Persistent.__setattr__(self, name, value) else: raise BrokenModified("Can't change broken objects") def __repr__(self): return "<persistent broken %s.%s instance %r>" % ( self.__class__.__module__, self.__class__.__name__, self._p_oid) def __getnewargs__(self): return self.__Broken_newargs__ def persistentBroken(class_): try: return class_.__dict__['__Broken_Persistent__'] except KeyError: class_.__Broken_Persistent__ = ( type(class_.__name__, (PersistentBroken, class_), {'__module__': class_.__module__}, ) ) return class_.__dict__['__Broken_Persistent__']