Steve Holden wrote: > Peter Otten wrote: >> perfr...@gmail.com wrote: >> >>> i am using nested defaultdict from collections and i would like to >>> write it as a pickle object to a file. when i try: >>> >>> from collections import defaultdict >>> x = defaultdict(lambda: defaultdict(list)) >>> >>> and then try to write to a pickle file, it says: >>> >>> TypeError: can't pickle function objects >>> >>> is there a way around this? it's simply a dictionary that i want to >>> write to file.. this works no problems with ordinary dicts. >> >> The error message is misleading. You can pickle your defaultdict if you >> use a "normal" function instead of the lambda: >> >> $ cat pickle_defaultdict.py >> import sys >> from collections import defaultdict >> from cPickle import dumps, loads >> >> if "--lambda" in sys.argv: >> make_inner = lambda: defaultdict(list) >> else: >> def make_inner(): >> return defaultdict(list) >> >> d = defaultdict(make_inner) >> d[1][2].append(42) >> e = loads(dumps(d)) >> print e == d >> >> $ python pickle_defaultdict.py >> True >> $ python pickle_defaultdict.py --lambda >> Traceback (most recent call last): >> File "pickle_defaultdict.py", line 13, in <module> >> e = loads(dumps(d)) >> File "/usr/lib/python2.5/copy_reg.py", line 69, in _reduce_ex >> raise TypeError, "can't pickle %s objects" % base.__name__ >> TypeError: can't pickle function objects >> > But can you unpickle the objects you pickle? I believe that functions > are references relative to the modules they come from, and so won't be > found unless the same module can be imported at unpickle time. Could be > wrong, haven't read the source, but I understand that functions work the > same as classes.
Indeed, what is stored in the pickle is the module and function name, not the byte code: >>> from cPickle import dumps, loads >>> def f(): print "original" ... >>> s = dumps(f) >>> def f(): print "updated" ... >>> g = loads(s) >>> g() updated That limits pickle as an exchange format to installations that provide compatible versions of the pickled classes and functions. Do you think that would be a problem for the OP? Peter -- http://mail.python.org/mailman/listinfo/python-list
