PyCQA/flake8-bugbear

Proposed Check: Flag Improper Use of string.find()

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#170 opened on May 22, 2021

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enhancementhelp wanted

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Description

Title: Flag Improper Use of string.find()

Description The string.find() method is easy to mis-use. A common error is:

mystring='abc'
if mystring.find('def'):
  print("def is contained in {}".format(mystring)

The issue is that if string.find fails, it returns -1, which is "truthy". If string.find() locates the output at the beginning of the line, it returns 0 which is "false".

mystring='abc'
if mystring.find('a'):
  print("a is in {}".format(mystring))
else:
  print('a is not in {}'.format(mystring))

It would be awesome if flake8-bugbear could flag any logical test involving string.find() that does not compare to a numerical value.

Contributor guide

Research direction
Study existing checkers in flake8 bugbear (e.g., B005). Write a new visitor that uses 'ast.Call' to find calls to 'str.find' and checks if they are used in a boolean context (e.g., inside an 'if' statement without comparison). Ensure the check flags cases where 'str.find' is used directly without comparing to 1 or 0.
Tech stack
python
Domain
devtools
Issue type
Feature
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
PythonGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85