Statement metadata¶

A metadata block can attach to any statement, not just a def or class — the same ; syntax Metadata blocks introduces works on a plain assignment, an if, a for, or any other statement a suite can contain.

Suppressing one check on one statement¶

Python's # noqa and # type: ignore comments only work as a trailing comment on the exact reported line: move the statement to a new line during a refactor and either the check comes back silently or the comment now silently suppresses whatever new statement lands under it. Neither is checked against a real list of checks, so a typo'd code (# noqa: E50 for E501) suppresses nothing and reports nothing.

ignore is a metadata block like any other, parsed as part of the statement's own grammar rather than floating text beside it:

x: int = 5; ignore: unused_variable

The same block can stand alone on the line right after the statement it covers, attaching the same way:

x: int = 5
; ignore: unused_variable

A misspelled check name — ignore: unused_varible — is the linter's own error, the same way an unknown field name already is elsewhere, not a silently ineffective comment.

Documenting a compound statement¶

When a metadata block is the first line of a suite a statement just opened, it attaches to that statement's own header rather than to anything inside the suite:

def transfer(amount: float, from_account: str, to_account: str) -> none:
    ; "Move money between two accounts."
    ...

The same statement can use the triple-quoted shorthand instead — see Triple-quoted strings are docstring shorthand.

No runtime reflection¶

Unlike a class member or a function parameter, an ordinary statement's metadata has no property that reads it back at runtime: fields() walks a class's, trait's, or module's members (see Member metadata), and Callable.parameters walks a function's own parameters (see Parameter metadata), but a local assignment or a for loop is neither. Its metadata exists for the reader and the linter alone.