[Python-ideas] [Python-3000] PEP 3107 Function Annotations: overloadable -> (original) (raw)

Josiah Carlson jcarlson at uci.edu
Tue Jan 2 07:34:41 CET 2007

Tony Lownds <tony at pagedna.com> wrote:

On Jan 1, 2007, at 5:39 PM, Josiah Carlson wrote: > Given a reading of version 53169 of PEP 3107, I see no reason to even > offer a returns attribute, automatic method call, etc. PEP 3107 > already defines the annotation to be specified as a dictionary of > named > argument names, with a key of 'return' for the annotation of the > return > annotation. Is there any reason why this isn't sufficient? > > Even in the context of the signature PEP 362, there is no need for > returns, as an annotation-consuming library would check the > signature object for argument annotations, and the funcannotations > dictionary for the 'return' key for any return annotations. Something got lost in the movement between lists... returns wasn't going to supplant or alter funcannotations or PEP 362 in any way. returns was proposed as the special method attached to a new operator (->). That operator could be used to write expressions that look like a function signature. Here's Kay's original email. http://mail.python.org/pipermail/python-list/2007-January/420774.html

-1 on the -> operator as specified in the email you link. There is no reason to add aribtrary operators for call-site annotations. PEP 3107 has already defined the syntax for function definition site annotations as follows...

def name(argument=default:annotation) -> annotation:
    body

While PEP 3107 has not been formally accepted (according to the web page), the ideas contained received general approval from more or less everyone involved in the py3k discussion, or at least more or less everyone who has written and/or consumed annotations in the past.

The mail you link, talks about an arbitrary -> operator for call-site annotations. Without seeing actual use-cases where a -> operator would be useful in the real-world, I can't help but be -1 on the -> operator and -1 on the returns method.

Use-case(s) before syntax and semantics,

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