Allow start parameter in Python's sum

[bgrenet]

From Python 3.8, the start parameter of the built-in function sum can be given as a keyword argument. For instance:

>>> sum([1,2,3], start=1)
7
>>> sum([[1],[2]], start=[])
[1, 2]

Sage's symbolic_sum, imported as sum and overwriting the original sum, does not pass this keyword argument. Hence in Sage:

>>> sum([1,2,3], start=1)
6
>>> sum([[1],[2]], start=[])
Traceback (most recent call last):
...
TypeError: unsupported operand type(s) for +: 'int' and 'list'

Component: misc

Keywords: sum

Author: Bruno Grenet

Branch/Commit: e2ae675

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/34007

[bgrenet]

Author: Bruno Grenet

[bgrenet]

New commits:

e2ae675

Pass the start keyword parameter

[bgrenet]

Commit: e2ae675

[bgrenet]

Branch: u/bruno/sum_with_start_keyword

[mkoeppe]

Reviewer: Matthias Koeppe

[vbraun]

Changed branch from u/bruno/sum_with_start_keyword to e2ae675