[Python-Dev] PEP 457: Syntax For Positional-Only Parameters (original) (raw)

Georg Brandl g.brandl at gmx.net
Wed Oct 9 17:09:47 CEST 2013

Am 09.10.2013 16:53, schrieb Larry Hastings:

On 10/09/2013 04:26 PM, Georg Brandl wrote:

I realize you are -1 on the proposal in general, but I'd be very interested if you could propose an alternate approach where I didn't need "a new spelling for None" as you put it. I think I would make Steven's proposed syntax mandatory: let the implementor of the function decide which value stands for "not given" -- just like we do in the C version, BTW. But that's not how addch works. addch counts how many arguments it received; if it is called with one or two, it does one thing, and if it's called with three or four it does something else. You can't duplicate these semantics with

Well, why should a function that requires counting arguments even in C code not be implemented using *args?

Documentation can cope fine, in the case of range() with two signatures.

Similarly, you can't accurately express the semantics of range's arguments using default values. PyPy's approach is approximately like this:

def range(x, y=None, step=None): step = 1 if step is None else step if y is not None: start, stop = x, y else: start, stop = 0, x But now introspection information on range() is inaccurate and unhelpful. (Not to mention, they allow specifying step without specifying y, by using keyword arguments.) My goal in writing the PEP was to codify existing practice, which meant reflecting these (annoying!) corner cases accurately.

These are only two, one of them being exceedingly obscure. The hobgoblin comes to mind :)

cheers, Georg

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