fix tab-completion for methods injected by MorphismMethods

[mwageringel]

For Cython classes that implement morphisms, the methods from MorphismMethods of the respective category are magically attached to elements of the class. However, tab-completion does not work on them.

For example, sage.categories.rings defines the morphism methods extend_to_fraction_field and is_injective:

sage: R.<x,y> = QQ[]
sage: f = R.hom([x, y+1], R)
sage: f.extend_to_frac<TAB>  # should complete to f.extend_to_fraction_field
sage: f.is_injec<TAB>  # should complete to f.is_injective

This is fixed by improving the corresponding __dir__ method.

Component: categories

Author: Markus Wageringel

Branch/Commit: 23cf6e7

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/29776

[mwageringel]

Branch: u/gh-mwageringel/29776

[mwageringel]

Author: Markus Wageringel

[mwageringel]

Commit: 23cf6e7

[mwageringel]

New commits:

23cf6e7

29776: fix tab-completion for morphism methods

[tscrim]

comment:2

Does the affect the method lookup time (the time it takes to call the methods) when the code is being run? For example, does it make something like 3.divides(9) slower?

[mwageringel]

comment:3

Method lookup does not actually call __dir__, which would be inefficient as __dir__ returns a list. In fact, I am not sure if it is used for anything but tab-completion. The Python documentation says that

*[...] dir() is supplied primarily as a convenience for use at an interactive prompt [...]*

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:4

Thanks. I couldn't find any information if that was used during method lookup (cf. __getattr__, __getattribute__). That gave me an idea to test, and the __dir__ is indeed only called on tab completion. Which also makes sense given its return type. Sorry for the dumb question. LGTM.

[vbraun]

Changed branch from u/gh-mwageringel/29776 to 23cf6e7