[Python-Dev] Type hints -- a mediocre programmer's reaction

[Ronan Lamy]

Le 23/04/15 14:55, Paul Sokolovsky a écrit :
> Hello,
>
> On Thu, 23 Apr 2015 09:15:44 -0400
> Daniel Holth <dholth at gmail.com> wrote:
>
> []
>
>>>> Also ask why no one used type specifier, they are possible since
>>>> Python 3.0 ?
>>>> Because it is the wrong way for Python.
>>>
>>> That's an example of how perceptions differ. In my list, everyone(*)
>>> uses them - MyPy, MicroPython, etc. Even more should use them (any
>>> JIT module, which are many), but sit in the bushes, waiting for a
>>> kick, like PEP484 provides.
>>
>> It's OK that type hints are only to assist the programmer.
>
> Yes, it's OK to have a situation where type hints assist only a
> programmer. It's not OK to think that type hints may be useful only for
> programmer, instead of bunch more purposes, several of which
> were already shown in the long previous discussion.
>
>> PyPy's FAQ
>> has an explanation of why type hints are not for performance.
>> http://pypy.readthedocs.org/en/latest/faq.html#would-type-annotations-help-pypy-s-performance
>
> You probably intended to write "why type hints are not for *PyPy's*
> performance". There're many other language implementations and modules
> for which it may be useful, please don't limit your imagination by a
> single case.

Those points apply to basically any compliant implementation of Python 
relying on speculative optimisation. Python is simply too dynamic for 
PEP484-style hints to provide any useful performance improvement targets.

> And speaking of PyPy, it really should think how to improve its
> performance - not of generated programs, but of generation itself. If
> compilation of a trivial program on a pumpy hardware takes 5 minutes
> and gigabytes of RAM and diskspace, few people will use it for other
> purposes beyond curiosity. There's something very un-Pythonic in
> waiting 5 mins just to run 10-line script. Type hints can help here
> too ;-) (by not wasting resources propagating types thru the same old
> standard library for example).

Sorry, but that's nonsense. PyPy would be a seriously useless 
interpreter if running a 10-line script required such a lengthy 
compilation, so, obviously, that's not what happens.

You seem to misunderstand what PyPy is: it's an interpreter with a 
just-in-time compiler, not a static compiler. It doesn't generate 
programs in any meaningful sense. Instead, it interprets the program, 
and when it detects a hot code path, it compiles it to machine code 
based on the precise types it sees. No resources are wasted on code that 
isn't actually executed.