Ian Kelly <ian.g.ke...@gmail.com> writes:
> Except that since we're discussing design for multiple inheritance,
> the positional argument "spam" is inappropriate. All arguments should
> be passed by keyword; the DolorSitAmet.__init__ method cannot be
> certain that LoremIpsum will be the next class in the MRO, and the
> actual next class might not expect spam to be the first positional
> argument.
You're right. That also allows us to stop handling unknown positional
arguments.
This does make it troublesome to design the function signature though,
and I can see why people balk at how to deal with the semantics of
‘super’ in Python 2::
class LoremIpsum(object):
def __init__(self, **kwargs):
spam = kwargs.pop('spam')
do_something_important_with(spam)
super(LoremIpsum, self).__init__(**kwargs)
class DolorSitAmet(LoremIpsum):
def __init__(self, **kwargs):
self.eggs = kwargs.pop('eggs')
self.beans = kwargs.pop('beans')
super(DolorSitAmet, self).__init__(**kwargs)
That's awful :-( because the initialiser's signature no longer shows any
sign of which parameters matter for this class.
It also sucks to need ‘dict.pop('name')’, instead of just ‘name’.
Keyword-only parameters make this easier and clearer::
class LoremIpsum:
def __init__(self, *, spam, **kwargs):
spam = kwargs.pop('spam')
do_something_important_with(spam)
super().__init__(**kwargs)
class DolorSitAmet(LoremIpsum):
def __init__(self, *, eggs=4, beans=None, **kwargs):
self.eggs = eggs
self.beans = beans
super().__init__(**kwargs)
I guess that's yet another reason to advocate Python 3 for all new code.
--
\ “One time a cop pulled me over for running a stop sign. He |
`\ said, ‘Didn't you see the stop sign?’ I said, ‘Yeah, but I |
_o__) don't believe everything I read.’” —Steven Wright |
Ben Finney
--
https://mail.python.org/mailman/listinfo/python-list
