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",
}
# -4: [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.