anomalous-backslash-in-string / W1401

Message emitted:

Anomalous backslash in string: '%s'. String constant might be missing an r prefix.

Description:

Used when a backslash is in a literal string but not as an escape.

Problematic code:

string = "\z"  # [syntax-error]

Correct code:

double_escape.py:

string = "\\z"

existing_escape_sequence.py:

string = "\t"

r_prefix.py:

string = r"\z"

Additional details:

\z is same as \\z because there's no escape sequence for z. But it is not clear for the reader of the code.

The only reason this is demonstrated to raise syntax-error is because pylint's CI now runs on Python 3.12, where this truly raises a SyntaxError. We hope to address this discrepancy in the documentation in the future.

Related links:

• String and Bytes literals

• Long form stackoverflow explanation

Created by the string checker.