Fix Python int problem with exp_integral

[kcrisman]

In #11143 we weren't careful about Python ints. There are lots of examples of this, so one will want to go through the whole file.

sage: exp_integral_e(int(3),0)
0
sage: exp_integral_e(3,0)
1/2

Depends on #17130

CC: @benjaminfjones @burcin @eviatarbach

Component: symbolics

Author: Jeroen Demeyer

Branch/Commit: 68c545a

Reviewer: Ralf Stephan

Issue created by migration from https://trac.sagemath.org/ticket/14766

[eviatarbach]

comment:3

I'm guessing this occurs in other files too.

I think it's unreasonable to expect everyone adding symbolic functions to worry about this, and certainly users to be aware of it; maybe we could make BuiltinFunction.__call__ automatically convert int to Integer? Or have it raise an error if an int is in the parameters? Allowing int into _eval_ causes other problems too, such as getting expressions with int pyobjects in them, making arithmetic slower, etc.

At the very least, we could temporarily add from future import division in all files that implement symbolic functions; then exact answers wouldn't be returned in all cases where they should, but at least mathematically wrong answers wouldn't occur.

[benjaminfjones]

comment:4

I think my preference would be either raising a TypeError (and clearly documenting what the allowed types are) or doing Python 3 style division. I don't like the idea of adding an implicit coercion int -> Integer.

If we do type checking in BuiltinFunction.__call__, we should make sure that there isn't a significant performance penalty.

[jdemeyer]

Branch: u/jdemeyer/ticket/14766

[jdemeyer]

Author: Jeroen Demeyer

[jdemeyer]

Commit: 68c545a

[jdemeyer]

Dependencies: #17130

[jdemeyer]

New commits:

6d10729	Simplify numerical evaluation of BuiltinFunctions
b6e1ed4	Merge remote-tracking branches 'origin/u/jdemeyer/ticket/17131' and 'origin/u/jdemeyer/ticket/17133' into ticket/17130
382f97a	Merge branch 'u/jdemeyer/ticket/17130' of trac.sagemath.org:sage into 6.5beta1
7265989	17130: reviewer's patch: fix typo
c47dbd4	Fix Trac #17328 again in a better way
a486db2	Call the factorial() method of an Integer
68c545a	Fix bugs due to Python 2 int division

[rwst]

Reviewer: Ralf Stephan

[rwst]

comment:10

Looks fine and passes tests in functions/.

[vbraun]

Changed branch from u/jdemeyer/ticket/14766 to 68c545a