Enforce using `.setdefault()`

[sobolevn]

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.

[adambenali]

Should this be closed for the same reasons as #1084 ?

[sobolevn]

Yes, thank you!

[sobolevn]

Or should it? Let's leave it open for now. I will have to make a small research.

[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.

[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