Well, I finally ran into a Python Unicode problem, sort of

[Alain Ketterlin]

John Ladasky <john_ladasky at sbcglobal.net> writes:

> from math import pi as π
> [...]
> c = 2 * π * r

> Up until today, every character I've tried has been accepted by the
> Python interpreter as a legitimate character for inclusion in a
> variable name. Now I'm copying a formula which defines a gradient. The
> nabla symbol (∇) is used in the naming of gradients. Python isn't
> having it. The interpreter throws a "SyntaxError: invalid character in
> identifier" when it encounters the ∇.

The rules are at
https://docs.python.org/3.5/reference/lexical_analysis.html#identifiers

To me it makes a lot of sense to *not* include category Sm characters in
identifiers, since they are usually used to denote operators (like +).
It would be very confusing to have a variable named ∇f, as confusing as
naming a variable a+b or √x.

-- Alain.