unicode as valid naming symbols

[MRAB]

On 2014-03-25 18:30, Mark H Harris wrote:
> greetings, I would like to create a lamda as follows:
>
> √ = lambda n: sqrt(n)
>
>
> On my keyboard mapping the "problem" character is alt-v which produces
> the radical symbol. When trying to set the symbol as a name within the
> name-space gives a syntax error:
>
>   >>> from math import sqrt
>   >>>
>   >>> √ = lambda n: sqrt(n)
> SyntaxError: invalid character in identifier
>   >>>
>   >>>
>
> however this works:
>
>   >>>
>   >>> λ = lambda n: sqrt(n)
>   >>>
>   >>> λ(2)
> 1.4142135623730951
>   >>>
>
>     The question is which unicode(s) are capable of being proper name
> characters, and which ones are off-limits, and why?
>
It's explained in PEP 3131.

Basically, a name should to start with a letter (this has been extended
to include Chinese characters, etc) or an underscore.

λ is a classified as Lowercase_Letter.

√ is classified as Math_Symbol.