var(['x','y']) should work but doesn't

[williamstein]

We were very surprised that var(['x','y']) doesn't work at the JMM QA session.

Apply attachment: trac_12247_var_construction-fix_typo.patch

CC: @vbraun

Component: symbolics

Keywords: var

Author: Volker Braun

Reviewer: Burcin Erocal

Merged: sage-5.0.beta0

Issue created by migration from https://trac.sagemath.org/ticket/12247

[burcin]

comment:1

This probably broke while fixing #7496.

[vbraun]

Author: Volker Braun

[vbraun]

comment:2

Well I was not aware that its supposed to work and the docstring doesn't mention it. The syntax

var('x, y')

is more compact imho. But then, why not allow a list/tuple of strings. Attached patch implements this.

[nbruin]

comment:3

The pythonic thing would be to realize that the important part of the list here is that it is an iterable and hence accepting an iterable might be the right thing to do. But since strings are iterable too, this doesn't work.

So either lists or strings would need to be special cased. This breaks subclassing (if someone writes a class that is supposed to mimic strings or lists, how do you tell which is which? isinstance doesn't work on builtins, and multiple inheritance would mean you would not necessarily be able to decide based on that anyway. Look in the mro which of list or str you meet first?)

Perhaps safer is to accept var('x','y') and hence also var(*['x','y']).

[vbraun]

comment:4

You are not supposed to use var() from code, so I don't think accepting more general iterables is particularly desirable.

[vbraun]

Updated patch

[vbraun]

comment:5

Attachment: trac_12247_var_construction.patch.gz

The new patch makes var a variadic function, so var('x','y') works as well.

[burcin]

fix typo in Volker's patch - apply only this one

[burcin]

Changed keywords from none to var

[burcin]

comment:6

Attachment: trac_12247_var_construction-fix_typo.patch.gz

I attached a new patch attachment: trac_12247_var_construction-fix_typo.patch which fixes a typo tree -> three in Volker's patch.

Volker's changes look good to me. I am switching this to a positive review.

[burcin]

Reviewer: Burcin Erocal

[jdemeyer]

Merged: sage-5.0.beta0