Steven Bethard wrote:
> -------------------------
> UserDict.DictMixin.update
> -------------------------
...
> To clean this up, we'd need the ability to identify self and dict as
> positional only arguments. AFAICT, the current proposal doesn't solve
> this problem. Off the top of my head, I don't see an easy way of
> supporting this either...
One way would be to expand assignment to support positional argument to
parameter matching when the sequence on the left is parenthesised:
def __init__(*args, **kwargs):
(self, other=None) = args
...
The signature info would still be lacking details on self & other, but the
kwarg conflict would be addressed.
Taking this idea one step further, the info could be moved back into the
signature by doing:
def __init__(*(self, other=None), **kwargs):
...
Which actually suggests an alternate approach for keyword-only arguments:
permitting argument expansion in a tuple after the **.
Then you'd have:
def f(a, *(b, c=1, *args), **(d, e=2, **kwds)):
# Silly function
'a' would be a normal positional-or-keyword argument
'b' would be a required positional-only argument
'c' would be an optional 3rd positional-only argument
'args' would contain any positional arguments after the 3rd
'd' would be a required keyword-only argument
'e' would be an optional keyword-only argument
'kwds' would contain any keyword arguments other than 'a', 'd' or 'e'
> ----------------------
> UserDict.DictMixin.pop
> ----------------------
...
> you still wouldn't know if "default" was None from the default in the
> signature or because the value None was supplied by the caller.
Making this distinction is where sentinel objects and identity tests are handy:
_pop_sentinel = object()
def pop(self, key, default=_pop_sentinel):
try:
value = self[key]
except KeyError:
if default is not self._pop_sentinel:
return default
raise
del self[key]
return value
(IOW, this can be made simpler without touching Python's syntax)
Cheers,
Nick.
--
Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
---------------------------------------------------------------
http://www.boredomandlaziness.org
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