difference between PermutationGroup.has_element and PermutationGroup.__contains__

[Martin R]

I just found

{{{

    def __contains__(self, item):
        """
        Return whether ``item`` is an element of the group.

...

    def has_element(self, item):
        """
        Returns boolean value of ``item in self`` - however *ignores*
        parentage.

...

        """

        return item in self

}}}

Isn't has_element just an alias of __contains__?

Martin

[davida...@gmail.com]

As you noticed, the difference between these two methods is very thin. The special method "__contains__" is necessary because it is called whenever the keyword "in" is used. I think that the code could have been simplified to:

{{{

    def __contains__(self, item):
        """
        Return whether ``item`` is an element of the group.

...

    has_element = __contains__

}}}

Why wasn't it done like this before? I don't know. Is there a better practice? I don't know.

What I know is that if you implement a new structure following the Parent/Element framework (for example:

https://doc.sagemath.org/html/en/thematic_tutorials/coercion_and_categories.html), the __contains__ method should be already available right out of the box.

[Martin R]

Exactly this is what I meant with "alias", and why I think that its documentation is misleading, if not wrong.  I just checked, has_element is not used in the sage library at all.  I thus propose to deprecate it.

[Kwankyu Lee]

On Tuesday, May 10, 2022 at 6:35:10 AM UTC+9 axio...@yahoo.de wrote:

Exactly this is what I meant with "alias", and why I think that its documentation is misleading, if not wrong.  I just checked, has_element is not used in the sage library at all.  I thus propose to deprecate it.

+1. But first survey use of `has_element` throughout sage library, to balance. 

 

[Martin R]

As I said, it is unused.  This is now https://trac.sagemath.org/ticket/33831