PyCQA/flake8-bugbear

B006: Case where mutable default arguments are not detected

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#253 opened on Apr 10, 2022

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Description

I realized that when using Python built-in dataclasses, the following scenario is not detected:

from dataclasses import dataclass

@dataclass
class MyClass:
    val = []  # Mutable data structure

Given the presence of the dataclass decorator, the signature of the __init__ method for MyClass is the following one:

def __init__(self, val = []):

I have seen that the rule B006 is supposed to detect issues where mutable data structures are used in a function signature. This is a slightly different scenario but with the same output if this effect is not intended. I could not find any related issue. Was this issue reported before?

Contributor guide

Research direction
Investigate how B006 currently detects mutable default arguments in function signatures, then extend the check to also inspect the generated ` init ` method of dataclasses. Look at the AST representation of a dataclass and analyze the ` init ` signature for mutable defaults.
Tech stack
python
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Pythonflake8dataclasses
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70