[Python-ideas] Optional static typing -- the crossroads

[Sunjay Varma]

On Aug 15, 2014 2:55 PM, "Łukasz Langa" <lukasz at langa.pl> wrote:
>
> On Aug 15, 2014, at 11:43 AM, Sunjay Varma <varma.sunjay at gmail.com> wrote:
>>
>> Hi all,
>> Has the syntax for specifying type been fully decided on already?
>>
>> Using brackets may confuse new Python programmers. (…) Other languages
use angle brackets to specify types.
>
>
> I also agree that angle brackets would be nicer. Guido decided against it
for pragmatic reasons:
> 1. angle brackets would create Python source code incompatible with any
version lower than 3.5

I'm all for compatibility, but Python 3 already breaks compatibility with
Python 2. Why not add this feature in Python 4 (or whatever the next
breaking release is) and do it "right" the first time. I don't think it
makes sense to start muddling up the different semantic meanings of
Python's operations just because we think it will break in an older
version.

This is such a big and important change. It deserves its own syntax (and if
necessary a new version number as well).

> 2. angle brackets would complicate the lexer (normally you expect < and >
to be spaced, in this case it wouldn’t)
> 3. angle brackets would require a new mechanism in Python to store this
kind of expression within the type; this is still true for generics
expressed with square brackets but at least you can use the existing nuts
and bolts of Python classes

Angle brackets were just a suggestion as they are used frequently by other
languages. Even braces would be more appropriate as they're already built
into the lexer and dict{int, str} clearly means something different than
dict[int, str].

>
> All in all, this is more trouble than it’s worth.

I can understand that it's easier to use what's already there, but I don't
agree with doing something just because it's easier. Especially when the
side effects are not at all appealing.

Sunjay
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