Hello all!
I have the following weird problem and since I am new to Python I somehow cannot figure out an elegant solution. The problem reduces to the following question:
How to pickle a collections.defaultdict object that has set the default_factory property?
For Example (from the IDLE console): - >>> words = collections.defaultdict(lambda: 1)
-
>>> f = file("temp","w")
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>>> pickle.dump(words,f)
-
-
Traceback (most recent call last):
-
File "<pyshell#77>", line 1, in <module>
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pickle.dump(words,f)
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File "C:\Python25\lib\pickle.py", line 1362, in dump
-
Pickler(file, protocol).dump(obj)
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File "C:\Python25\lib\pickle.py", line 224, in dump
-
self.save(obj)
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File "C:\Python25\lib\pickle.py", line 331, in save
-
self.save_reduce(obj=obj, *rv)
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File "C:\Python25\lib\pickle.py", line 401, in save_reduce
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save(args)
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File "C:\Python25\lib\pickle.py", line 286, in save
-
f(self, obj) # Call unbound method with explicit self
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File "C:\Python25\lib\pickle.py", line 562, in save_tuple
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save(element)
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File "C:\Python25\lib\pickle.py", line 286, in save
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f(self, obj) # Call unbound method with explicit self
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File "C:\Python25\lib\pickle.py", line 748, in save_global
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(obj, module, name))
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PicklingError: Can't pickle <function <lambda> at 0x00C030B0>: it's not found as __main__.<lambda>
-
-
If I repeat the same with words = collections.defaultdict() everything goes fine..
-
-
In my real code I have a class that has an object property which is a defaultdict with the same default_factory set. I want to dump an object from this class with pickle and I get the following error:
-
Traceback (most recent call last):
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File "BayesianFilter.py", line 125, in <module>
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pickle.dump(bf,file(sys.argv[1]+'.bf','w'))
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File "C:\Python25\lib\copy_reg.py", line 69, in _reduce_ex
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raise TypeError, "can't pickle %s objects" % base.__name__
-
TypeError: can't pickle function objects
If I do not set a default_factory in the constructor of the defaultdict object everything goes ok.. which makes me think that the problem is exactly this.
I know that Pickle cannot dump objects that have function properties. I did not find a way to unset the default_factory property from the defaultdict object before dumping though.. Neither I found a way to set it again after a defaultdict object was created once..
Does anyone have a clue how to resolve this issue elegantly?
Thanks for the help
3  5999 
I think I understand what the issue is, but how to solve it I don't know. Why do you need to pickle the object? I have never found a use for that module myself, so I would be interested to know what it is being used for in your case. There is probably a more elegant way to save information from the program than using the pickle module.
I think I understand what the issue is, but how to solve it I don't know. Why do you need to pickle the object? I have never found a use for that module myself, so I would be interested to know what it is being used for in your case. There is probably a more elegant way to save information from the program than using the pickle module.
Basically, I need some sort of persistence layer for my program. I.e. to store objects and load them from files afterwards. I have read about the pickle module and it seems a good solution to me. If anyone knows a better way to do this, I would like to know.
solution: - def give_me_1(): return 1
-
words = collections.defaultdict(give_me_1)
-
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# the rest was good
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f = file("temp","w")
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pickle.dump(words,f)
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