Path: ...!fu-berlin.de!uni-berlin.de!not-for-mail From: ram@zedat.fu-berlin.de (Stefan Ram) Newsgroups: comp.lang.python Subject: Re: Struggling to understand Callable type hinting Date: 18 Jan 2025 16:11:05 GMT Organization: Stefan Ram Lines: 27 Expires: 1 Jan 2026 11:59:58 GMT Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Trace: news.uni-berlin.de fpIBH9MyUD+Hdoua1JNqVgD0DHq4SI8lEI54ovrqJ9ZNIP Cancel-Lock: sha1:F/SSt46emWEUbhmLWSqlx4whvAE= sha256:OkMDKwBuCCSyLzyBgnA6DxTBNf7OdtSNL3/8Ui785lg= X-Copyright: (C) Copyright 2025 Stefan Ram. All rights reserved. Distribution through any means other than regular usenet channels is forbidden. It is forbidden to publish this article in the Web, to change URIs of this article into links, and to transfer the body without this notice, but quotations of parts in other Usenet posts are allowed. X-No-Archive: Yes Archive: no X-No-Archive-Readme: "X-No-Archive" is set, because this prevents some services to mirror the article in the web. But the article may be kept on a Usenet archive server with only NNTP access. X-No-Html: yes Content-Language: en-US Bytes: 2611 ram@zedat.fu-berlin.de (Stefan Ram) wrote or quoted: > @staticmethod > def _check_eof(method: Callable[Concatenate['BufferScanner', P], T]) -> Callable[Concatenate['BufferScanner', P], bool]: > def wrapper(self: 'BufferScanner', *args: P.args, **kwargs: P.kwargs) -> bool: "P" (ParamSpec) is resolved when the decorator is applied to any method. - "P" (ParamSpec) captures all parameters of the decorated method except for the first "self" parameter. "Concatenate['BufferScanner', P]" then adds the "BufferScanner" type as the first parameter, effectively representing the complete parameter list of the method. "T" (TypeVar) is inferred based on the return type of the method being decorated. So, those type variables are resolved based on the specific method the decorator is applied to, allowing for generic and reusable type annotations across different classes and methods (This "resolution" of a type name corresponds to the initialization of a traditional name. But a single type name can have multiple values when the wrapper is being applied to multiple methods - one value per application.)