arrays - Python, cPickle, pickling lambda functions

Question

I have to pickle an array of objects like this:

import cPickle as pickle
from numpy import sin, cos, array
tmp = lambda x: sin(x)+cos(x)
test = array([[tmp,tmp],[tmp,tmp]],dtype=object)
pickle.dump( test, open('test.lambda','w') )

and it gives the following error:

TypeError: can't pickle function objects

Is there a way around that?

Answer 1

The built-in pickle module is unable to serialize several kinds of python objects (including lambda functions, nested functions, and functions defined at the command line).

The picloud package includes a more robust pickler, that can pickle lambda functions.

from pickle import dumps
f = lambda x: x * 5
dumps(f) # error
from cloud.serialization.cloudpickle import dumps
dumps(f) # works

PiCloud-serialized objects can be de-serialized using the normal pickle/cPickle load and loads functions.

Dill also provides similar functionality

>>> import dill           
>>> f = lambda x: x * 5
>>> dill.dumps(f)
'x80x02cdill.dill
_create_function
qx00(cdill.dill
_unmarshal
qx01Uecx01x00x00x00x01x00x00x00x02x00x00x00Cx00x00x00sx08x00x00x00|x00x00dx01x00x14S(x02x00x00x00Nix05x00x00x00(x00x00x00x00(x01x00x00x00tx01x00x00x00x(x00x00x00x00(x00x00x00x00sx07x00x00x00<stdin>tx08x00x00x00<lambda>x01x00x00x00sx00x00x00x00qx02x85qx03Rqx04c__builtin__
__main__
Ux08<lambda>qx05NN}qx06tqx07Rqx08.'