Index notation for tensors should allow for unicode characters

[egourgoulhon]

In Sage 9.0, we have:

sage: E.<x,y> = EuclideanSpace()
sage: t = E.tensor_field(1, 1, [[x, 1], [0, y]])
sage: t['^μ_μ']
...
ValueError: index conventions not satisfied

Now, after the Python 3 switch, any unicode non-digit word-constituent character should be accepted, see ​this discussion. This is especially pertinent for tensor indices, since Greek letters are often used to denote them.

[mkoeppe]

Batch modifying tickets that will likely not be ready for 9.1, based on a review of the ticket title, branch/review status, and last modification date.

[mkoeppe]

New commits:

​ab2beb1

sage.tensor.modules.tensor_with_indices: Allow unicode indices (non-digit word constituents)

[egourgoulhon]

Thanks for this improvement! LGTM.

[mkoeppe]

Thanks!

[vbraun]

pdf docs don't build

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​4d8305f

src/sage/tensor/modules/tensor_with_indices.py: Use unicode escapes instead of characters in docstrings, so that pdf doc builds

[egourgoulhon]

Thanks for the fix.