Dubious or potentially invalid syntax
Quick Answer
Fix the flagged syntax — SyntaxWarnings often indicate a bug. Use == instead of is for value comparisons; use raw strings for regex patterns.
Production Risk
Medium — SyntaxWarning for invalid escapes becomes a SyntaxError in 3.12, breaking the code.
Raised for dubious syntax that is currently valid Python but may be unintentional, such as using `is` for value comparisons or invalid escape sequences in strings.
- 1Using `is` or `is not` to compare with a literal value (e.g. x is 0)
- 2Invalid escape sequence in a string literal (becomes SyntaxError in Python 3.12+)
Fix
Replace is with == for value comparisons
# Bad — raises SyntaxWarning if x is 0: ... # Good if x == 0: ... # For regex — use raw strings to avoid escape warnings import re pattern = re.compile(r'\d+') # raw string, no SyntaxWarning
Why this works
`is` tests identity, not equality; using it with literals is almost always a bug. Raw strings prevent unintended escape sequences.
import warnings
warnings.filterwarnings('error', category=SyntaxWarning)Invalid escape sequences that were SyntaxWarning in 3.6–3.11 became SyntaxError in 3.12.
Python Docs
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