[Python-3000] Draft pre-PEP: function annotations (original) (raw)

Phillip J. Eby pje at telecommunity.com
Sat Aug 12 04:52:57 CEST 2006

At 03:39 PM 8/12/2006 -0700, Talin <talin at acm.org> wrote:

Say I want to annotate a specific argument with two pieces of information, a type and a docstring. I have two metadata interpreters, one which uses the type information to restrict the kinds of arguments that can be passed in, and another which uses the docstring to enhance the generated documentation.

Now, lets say that these two metadata interpreters were written by two people, who are not in communication with each other. Each one decides that they would like to "play nice" with other competing metadata. So Author A, who wrote the annotation decorator that looks for docstrings, decides that not only will he accept docstring annotations, but if the annotation is a tuple, then he will search that tuple for any docstrings, skipping over any annotations that he doesn't understand. (Although how he is supposed to manage that is unclear - since there could also be other annotations that are simple text strings as well.) Author B, who wrote the type-enforcement module, also wants to play nice with others, but since he doesn't know A, comes up with a different solution. His idea is to create a system in which annotations automatically chain each other - so that each annotation has a "next" attribute referring to the next annotation. So programmer C, who wants to incorporate both A and B's work into his program, has a dilemma - each has a sharing mechanism, but the sharing mechanisms are different and incompatible. So he is unable to apply both A-type and B-type metadata to any given signature.

Not at all. A and B need only use overloadable functions, and the problem is trivially resolved by adding overloads. The author of C can add an overload to "A" that will handle objects with 'next' attributes, or add one to "B" that handles tuples, or both.

I've not bothered to reply to the rest of your email, since it depends on assumptions that I've already shown to be invalid.

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