too-many-positional-sub-patterns / E1903

Message emitted:

%s expects %d positional sub-patterns (given %d)

Description:

Emitted when the number of allowed positional sub-patterns exceeds the number of allowed sub-patterns specified in `__match_args__`.

Problematic code:

class Book:
    __match_args__ = ("title", "year")

    def __init__(self, title, year, author):
        self.title = title
        self.year = year
        self.author = author


def func(item: Book):
    match item:
        case Book("title", 2000, "author"):  # [too-many-positional-sub-patterns]
            ...

Correct code:

class Book:
    __match_args__ = ("title", "year")

    def __init__(self, title, year, author):
        self.title = title
        self.year = year
        self.author = author


def func(item: Book):
    match item:
        case Book("title", 2000, author="author"):
            ...

Related links:

• Python documentation

Created by the match_statements checker.