Why can't generators be pickled?

Question

Python\'s pickle (I\'m talking standard Python 2.5/2.6/2.7 here) cannot pickle locks, file objects etc.

It also cannot pickle generators and lambda expressions (or

Answer 1

You actually can, depending on the implementation. PyPy and Stackless Python both allow this (to some degree anyway):

Python 2.7.1 (dcae7aed462b, Aug 17 2011, 09:46:15)
[PyPy 1.6.0 with GCC 4.0.1] on darwin
Type "help", "copyright", "credits" or "license" for more information.
And now for something completely different: ``Not your usual analyses.''
>>>> import pickle
>>>> gen = (x for x in range(100))
>>>> next(gen)
0
>>>> pickled = pickle.dumps(gen)
>>>> next(pickle.loads(pickled))
1

In CPython it's also possible to create an iterator object to simulate a pickable generator.