Enforce using `.setdefault()`

Rule request

Thesis

One can write this code:

if "list" not in dictionary:
    dictionary["list"] = []

dictionary["list"].append("list_item")

But, it is an anti-pattern. Instead one should write:

dictionary = {}

dictionary.setdefault("list", []).append("list_item")

Related: https://docs.quantifiedcode.com/python-anti-patterns/correctness/not_using_setdefault_to_initialize_a_dictionary.html

This is a refactoring rule.

[sobolevn]

@ruwaid4 here you go:

• https://github.com/wemake-services/wemake-python-styleguide/issues/864
• https://github.com/wemake-services/wemake-python-styleguide/issues/1025
• https://github.com/wemake-services/wemake-python-styleguide/issues/1239

[ruwaid4]

@sobolevn Should this rule be implemented? If not, could you recommend us an issue to work on? We have looked at most of them but aren’t up to date on what should be implemented or not.