On 09/10/13 00:33, Larry Hastings wrote:
>
> I've contributed a new PEP to humanity. I include the RST for your
> reading pleasure below, but you can also read it online here:
>
> http://www.python.org/dev/peps/pep-0457/
Overall I'm in favour.
As a motivation for positional only parameters, consider:
Python 3.2:
>>> from decimal import Decimal
>>> d = Decimal(4)
>>> d.__add__(other=d)
Decimal('8')
Python 3.3:
>>> from decimal import Decimal
>>> d = Decimal(4)
>>> d.__add__(other=d)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: wrapper __add__ doesn't take keyword arguments
[snip]
> The obvious solution: add a new singleton constant to Python
> that is passed in when a parameter is not mapped to an argument.
> I propose that the value be called called ``undefined``,
> and be a singleton of a special class called ``Undefined``.
> If a positional-only parameter did not receive an argument
> when called, its value would be set to ``undefined``.
There is no need to create an "undefined" value.
Rather than define a parameter by assigning a fake value, just don't
define it. We already do this for non-parameter locals and it could be
extended to parameters.
'range' would be defined thus:
def range([start,] stop, [step], /):
try:
start
except UnboundLocalError:
start = 0
try:
step
except UnboundLocalError:
step = 1
...
Cheers,
Mark.
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