Pickling dynamically generated classes?

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I'm using type() to dynamically generate classes that will ultimately be pickled. The problem is that the un-pickling process needs the definition of the class in order to re-construct the object that has been pickled.

This is where I'm stuck. I don't know how to somehow provide the unpickler a way to generate an instance from a class that was dynamically generated.

Any hints appreciated.

Thanks!

Here's an example of the problem:

    >>> class Foo(object):
    ...     pass
    >>> g=type('Goo',(Foo,),{'run':lambda self,x: 2*x } )()
    >>> cPickle.dumps(g)

    PicklingError: Can't pickle <class '__main__.Goo'>: attribute lookup __main__.Goo failed

This evidently works, but only from dynamic classes created from a pickle-able base class (with find-able module definition):

import cPickle

class Foo(object): pass

def dynamic(): return type('Goo',(Foo,),{'run':lambda self,x: 2*x } )()

g=type('Goo',(Foo,),{'run':lambda self,x: 2*x , '__reduce__': lambda self: (dynamic,tuple()) } )()

gg=cPickle.loads ( cPickle.dumps(g) )
print gg.run(10)
pickle dynamic metaprogramming class python
6 Answers

Well, for the posterity; works with cloudpickle

import cloudpickle

class Foo(object):
    pass
g=type('Goo',(Foo,),{'run':lambda self,x: 2*x } )()
cloudpickle.dumps(g)
user_59131010
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