New submission from Alexandre Vassalotti <[EMAIL PROTECTED]>: The multiprocessing module modifies the global copyreg.dispatch_table to extend pickling to several built-in types (mostly callable types). In my humble opinion, this is unacceptable for a standard library module.
Here is an example of a behaviour change made by multiprocessing: >>> import pickle >>> pickle.dumps(str.isalpha) Traceback (most recent call last): ... _pickle.PicklingError: Can't pickle <class 'method_descriptor'>: attribute lookup builtins.method_descriptor failed >>> import multiprocessing.util >>> pickle.dumps(str.isalpha) b'\x80\x03cbuiltins\ngetattr\nq\x00cbuiltins\nstr\nq\x01X\x07\x00\x00\x00isalphaq\x02\x86q\x03Rq\x04.' There was some discussion in issue 558238 about allowing methods to be pickled. However, no consensus was reached. In addition, there is a bug in the method pickling support added by multiprocessing in Python 3.0: Python 2.6b1+ (trunk:64899:64900, Jul 13 2008, 13:33:02) [GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import multiprocessing.util, pickle >>> class A(object): ... def foo(self): pass ... >>> pickle.dumps(A().foo, 2) '\x80\x02c__builtin__\ngetattr\nq\x00c__main__\nA\nq\x01)\x81q\x02}q\x03bU\x03fooq\x04\x86q\x05Rq\x06.' >>> pickle.dumps(A.foo, 2) '\x80\x02c__builtin__\ngetattr\nq\x00c__main__\nA\nq\x01U\x03fooq\x02\x86q\x03Rq\x04.' Python 3.0b1+ (py3k:64876M, Jul 11 2008, 12:20:51) [GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import multiprocessing.util, pickle >>> class A(object): ... def foo(self): pass ... >>> pickle.dumps(A().foo, 2) Traceback (most recent call last): ... pickle.PicklingError: Can't pickle <class 'method'>: it's not found as builtins.method >>> pickle.dumps(A.foo, 2) Traceback (most recent call last): ... pickle.PicklingError: Can't pickle <function foo at 0xb7b1392c>: it's not found as __main__.foo A better solution for the interprocess communication needs of multiprocessing would be to define custom subclass of Pickler with extended support for built-in types. If needed, I am willing to extend the _pickle module in Python 3.0 to support modification to its "dispatch table", like the undocumented dispatch_table attribute in pickle.Pickler. ---------- components: Library (Lib) messages: 69615 nosy: alexandre.vassalotti priority: normal severity: normal status: open title: multiprocessing adds built-in types to the global copyreg.dispatch_table type: behavior versions: Python 2.6, Python 3.0 _______________________________________ Python tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue3350> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com