all Python 3Exceptionsexception

SyntaxWarning

built-in exceptions

Warns about dubious syntax (e.g. a suspicious comparison such as x is 1).

Syntax

raise SyntaxWarning

It is a warning, not an error: the compiler prints it once and keeps going, so an except block normally never sees it. The two classic triggers are comparing to a literal with is instead of ==, and an unrecognised escape sequence in a plain string — since Python 3.12 that emits SyntaxWarning, and an r-prefix fixes it. Run with -W error::SyntaxWarning if you want these spots to fail loudly instead of scrolling past.

Examples

try:
    raise SyntaxWarning
except SyntaxWarning as e:
    print(type(e).__name__)   # → SyntaxWarning

See also

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