Unicode identifiers in Python?

Question

Hi all,

I want to build a Python function that calculates,

and would like to name my summation function Σ. In a similar fashion, would like to use Π for product, and so on. I was wondering if there was a way to name a python function in this fashion?

def Σ (..):
 ..
 ..

That is, does Python support unicode identifiers, and if so, could someone provide an example for it?

Thanks!

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Original motivation for this was a piece of Clojure code I saw today that looks like,

(defn entropy [X]
      (* -1 (Σ [i X] (* (p i) (log (p i))))))

where Σ is a macro defined as,

(defmacro Σ
    ... )

and I thought that was pretty cool.

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BTW, to address a couple of comments about readability - with a lot of stats/ML code for instance, being able to compose operations with symbols would be really helpful. (Especially for really complex integrals et al)

φ(z) = ∫(N(x|0,1,1), -∞, z)

vs

Phi(z) = integral(N(x|0,1,1), -inf, z)

or even just the lambda character for lambda()!

Answer 1

(I think it’s pretty cool too, that might mean we’re geeks.)

You’re fine to do this with the code you have above in Python 3 (Works in my Python 3.1 interpreter anyway.). See:

• http://docs.python.org/py3k/reference/lexical_analysis.html#identifiers
• http://www.python.org/dev/peps/pep-3131/

But in Python 2, identifiers can only be letters, numbers and underscores.

• http://docs.python.org/reference/lexical_analysis.html#identifiers

Answer 2

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?