Custom unpickler and pickler for the shelve module

[furkanonder]

The goal of this enhancement is to make the shelve module more usable by accepting custom types of pickler and unpickler.

Example

The lambda functions can not be pickled by Python's pickle module. So, for that reason the shelve library also can’t do that.

The shelve module was unable to handle this situation.

import shelve
with shelve.open("test_file") as sh:
    squared = lambda x: x ** 2
    sh['test_key'] = squared

With the changes made here, the shelve module can easily overcome this issue.

import dill
import shelve

with shelve.open("test_file_2", pickler=dill.Pickler, unpickler=dill.Unpickler) as sh:
    squared = lambda x: x ** 2
    sh['test_key'] = squared

Previous discussion

• https://discuss.python.org/t/custom-unpickler-and-pickler-for-the-shelve-module/21178

Linked PRs

• gh-99631: Add custom loads and dumps support for the shelve module #99632
• gh-99631: Add custom loads and dumps support for the shelve module #118065