unused-format-string-key / W1301

Message emitted:

Unused key %r in format string dictionary

Description:

Used when a format string that uses named conversion specifiers is used with a dictionary that contains keys not required by the format string.

Problematic code:

"The quick %(color)s fox jumps over the lazy dog." % {"color": "brown", "action": "hops"}
# -1: [unused-format-string-key]

Correct code:

"The quick %(color)s fox %(action)s over the lazy dog." % {"color": "brown", "action": "hops"}

Created by the string checker.