I have read in a number of threads that Python pickle
/cPickle
cannot pickle lambda functions. However the following code works, using Python 2.7.6:
import cPickle as pickle
if __name__ == "__main__":
s = pickle.dumps(lambda x, y: x+y)
f = pickle.loads(s)
assert f(3,4) == 7
So what is going on? Or, rather, what is the limit of pickling lambdas?
[EDIT] I think i know why this code runs. I forgot (sorry!) i am running stackless python, which has a form of micro-threads called tasklets executing a function. These tasklets can be halted, pickled, unpickled and continued, so i guess (asked on the stackless mailing list) that it also provides a way to pickle function bodies.
Yes, python can pickle lambda functions… but only if you have something that uses copy_reg
to register how to pickle lambda functions -- the package dill
loads the copy_reg
you need into the pickle registry for you, when you import dill
.
Python 2.7.8 (default, Jul 13 2014, 02:29:54)
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>> import dill # the code below will fail without this line
>>>
>>> import pickle
>>> s = pickle.dumps(lambda x, y: x+y)
>>> f = pickle.loads(s)
>>> assert f(3,4) == 7
>>> f
<function <lambda> at 0x10aebdaa0>
get dill here: https://github.com/uqfoundation