Unicode identifiers in Python?

Question

I want to build a Python function that calculates,

Answer 1

Python 2.x does not support unicode identifiers, and consequently does not support Σ as an identifier. Python 3.x does support unicode identifiers, although many people will get cross if they have to edit source files with, for example, identifiers A and Α (latin A and greek capital alpha.) Sigma is often readable enough, but still, not as readable as the word sigma, so why bother?