[Python-Dev] Python Call Mechanism

[Michael Hudson]

Michael Hudson <mwh21@cam.ac.uk> writes:

> Guido van Rossum <guido@python.org> writes:
> 
> Then the following could be made essentially equivalent:
> 
> f(a,b,c=d,e=f)
> 
> dict = {c:d,e:f}
> f(a,b,**dict)

... except when you have stuff like

f(a,b=c,**kw)

Gruntle.  Maybe Python function calls are just complicated!  (Has
anyone looked at bytecodehacks.xapply? - and that doesn't even handle
*-ed and **-ed arguments...).

Hmm - the interaction of "a=b" style args & *-ed args is a bit
counter-intuitive, particularly as the "a=b" args syntatically have to
come before the *-ed args:

>>> def f(a,b,c,d):
...  return a,b,c,d
... 
>>> f(1,c=3,*(2,4))
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: keyword parameter 'c' redefined in call to f()
>>> f(1,b=3,*(2,4))
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: keyword parameter 'b' redefined in call to f()
>>> f(1,d=4,*(2,3))
(1, 2, 3, 4)

I humbly submit that This Is Wrong.  I haven't seen anybody complain
about it, which suggests to me that noone is using this combination,
and I propose either:

1) banning it
2) demanding that the *-ed arg precede the "a=b" args

Of course, if noone is using this "feature", then maybe this dusty
little corner of the language should be left undisturbed.

And I haven't even thought about default arguments yet...

about-to-make-an-opcode-called-BODGE_KEYWORD_ARGUMENTS-ly y'rs
M.

-- 
  nonono,  while we're making wild  conjectures about the behavior 
  of completely  irrelevant tasks,  we must not  also make serious 
  mistakes, or the data might suddenly become statistically valid.
                                        -- Erik Naggum, comp.lang.lisp