pi-lens/rules/tree-sitter-queries/python/is-vs-equals.yml

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# Is vs Equals for Literals
# Detects 'is' used with string/int literals (should use '==')
id: is-vs-equals
name: Is vs Equals for Literals
severity: warning
category: reliability
defect_class: correctness
inline_tier: blocking
language: python

message: "Using 'is' with literal — use '==' for value comparison"

description: |
  'is' checks identity (same object in memory), not equality.
  For strings and small ints, Python may intern them, making
  'is' appear to work, but it's unreliable and wrong.
  
  ✅ FIX: Use '==' for value comparison
  
  ```python
  if name == "admin":  # GOOD - value comparison
  if count == 0:  # GOOD - value comparison
  ```

query: |
  (comparison_operator
    (identifier)
    ("is")
    (string) @LITERAL)
  (comparison_operator
    (identifier)
    ("is not")
    (string) @LITERAL)
  (comparison_operator
    (identifier)
    ("is")
    (integer) @LITERAL)
  (comparison_operator
    (identifier)
    ("is not")
    (integer) @LITERAL)

metavars:
  - LITERAL

tags:
  - reliability
  - common-mistake
  - python-specific

examples:
  bad: |
    if name is "admin":  # BAD - identity check
    if count is 0:  # BAD - may work by accident
  
  good: |
    if name == "admin":  # GOOD
    if count == 0:  # GOOD
    if obj is None:  # OK - None is a singleton

has_fix: true
fix_action: replace_is_with_equals