[Python-ideas] PEP 484 (Type Hints) -- second draft

[Chris Barker]

On Mon, Mar 23, 2015 at 2:41 PM, Cameron Simpson <cs at zip.com.au> wrote:

> But it scales very badly; what of a 4 way if etc? It moves from a bit less
> readable to a nightmare.
>

in python one particular type or None is a very common idiom -- well worth
special casing. Somethign that could take or return 4 different types is a
far less usual case, we can be more verbose there.

Note that Cython and Pyrex default to "or NOne", and you have to do

func( int x not None)

if you don't want to allow the None. That's because None as a not-set-yet
value is so common. In this case, it's a mistake to make it the default, as
Cython does not generate checks later for None, so it can get ugly if you
don't specifically test for it in your code. None the less, it's very
useful.

-Chris






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