Pickling keyword arguments in Python 3

Question

Python 2 doc says:

Deprecated since version 2.3: Use function(*args, **keywords) instead of apply(function, args, keywords) (see Unpacking Argument Lists).

Pickle module requires the following syntax to define __reduce__ method to dump an object:

def __reduce__():
     return (<A callable object>, <A tuple of arguments for the callable object.>) 

(I know that the length of tuple returned from __reduce__ can be >2 but needs to be <=5. Considering the case of length 2 in the context of current question.)

This means it is not possible to pass keyword arguments to the callable object. In Python 2, I have the following work-around:

def __reduce__():
     return (apply, (<A callable object>, ((<args>,), <kwargs>))

However, builtins.apply has been removed in Python 3. Is there any other alternative to implementing my own version of builtins.apply in Python 3?

Answer 1

You can use functools.partial for this:

from functools import partial

def __reduce__():
     return (partial(<A callable object>, <kwargs>), ())