[Python-ideas] More alternate constructors for builtin type

[Cameron Simpson]

On 06May2019 18:47, Antoine Pitrou <solipsis at pitrou.net> wrote:
>On Mon, 6 May 2019 19:39:39 +0300
>Serge Matveenko <s at matveenko.ru> wrote:
>> On Mon, May 6, 2019 at 7:29 PM Guido van Rossum <guido at python.org> wrote:
>> > On Mon, May 6, 2019 at 11:14 AM Serhiy Storchaka <storchaka at gmail.com> wrote:
>> >> I do not propose to change the current behavior. I propose to add new
>> >> named constructors. In most cases default constructors can be used, but
>> >> in cases when we use type check or different tricks to limit the type of
>> >> the argument, we could use named constructors.
>> >>
>> >> Current named constructors:
>> >>
>> >> * dict.fromkeys()
>> >> * int.from_bytes()
>> >> * float.fromhex()
>> >> * bytes.fromhex()
>> >> * bytearray.fromhex()
>> >
>> > Understood. My point is that we won't be able to remove the original behavior, so we'd end up with two ways to do it. :-(
>>
>> With all respect, I disagree. There are ways to evolve Python such as
>> deprecation policies which proven to be effective. There are ways to
>> monitor current features adoption on PyPI to see whether it is safe to
>> remove deprecated things.
>
>The main constructors for built-in types are used so pervasively that
>there is no hope of actually removing such deprecated behavior.

I don't find that compelling. I for one would welcome a small suite of 
unambiguous factories that can't be misused. bytes() can easily be 
misused by accident, introducing bugs and requiring debug work. I'd be 
very happy for my own future code to be able to take advantage of hard 
to misuse constructors.

Of course we could all write tiny factories for these modes but (a) we'd 
all have to write and debug them and (b) they'de all have different 
spellings and signatures and (c) everyone else would not have easy 
access to them (yes, PyPI notwithstanding: finding a specific module in 
there can be haphazard) and (d) the bytes type is a natural place to 
have these constructors/factories.

All these arguments apply to the other types too.

Cheers,
Cameron Simpson <cs at cskk.id.au>