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Unicode identifiers in Python?

I want to build a Python function that calculates,

alt text

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!

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.

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)

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

or even just the lambda character for lambda()!

Answer*

(this answer is meant to be a minor addendum not a complete answer)

The additional gotcha to unicode identifiers (which @mike-desimone mentions and I discovered quickly when I thought this was a cool thread and switched to a terminal to play with it), is the multiple versions of each glyph are not equivalent, with regards to how you get to each glyph on each platform. For example Σ (aka greek capital letter sigma, aka U+03A3, [can't find a direct mac input method]) is fine, but unfortunately ∑ (aka **N-ary Summation**, aka **U+2211**, aka **opt/alt-w** using Mac OS X) is not a valid identifier.


 >>> Σ = 20
 >>> Σ
 20
but 

 >>> ∑ = 20
 File "<input>", line 1
 ∑ = 20
 ^
 SyntaxError: invalid character in identifier


Using Σ specifically (and probably unicode chars in general) as an identifier might generate some very hard to diagnose errors if you have multiple developers on multiple platforms contributing to your code, for example, debug this visually:

![∑ looks very similar to Σ, depending on the typeface selected][1]

The two glyphs are easier to differentiate on this page, but depending on the font used, this may not be the case.

Even the traceback isn't much clearer unless Σ is printed near the ∑ 

 File "~/Dev/play_python33/identifiers.py", line 12
 print(∑([2, 2, 2, 2, 2]))
 ^
 SyntaxError: invalid character in identifier

 [1]: https://i.sstatic.net/5rioo.png

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17

Another gotcha is that there are multiple glyphs that are equivalent. Define φ = 5, then φ is φ → True

endolith
– endolith

2018年01月30日 15:54:53 +00:00
Commented Jan 30, 2018 at 15:54
4

@endolith this is exactly what I discovered in horror today.

episodeyang
– episodeyang

2019年03月28日 00:00:14 +00:00
Commented Mar 28, 2019 at 0:00

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Unicode identifiers in Python?

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