default tuple unpacking?
peter at engcorp.com
Tue Sep 3 23:58:39 EDT 2002
Peter Hansen wrote:
> Huaiyu Zhu wrote:
>> It is often very convenient to have default arguments such as
>> def func(a, b, *c): ...
>> Is there a way to use this in statements too? Examples:
>> a, (b, *c), *d = e
Hmm... I think there might be an inconsistency or an unexpected
result in this. What if e already contains a tuple?
e = (1, 2, 3)
*a = e # a is ((1, 2, 3), )
That seems sensible, and it's just what happens if you pass
"e" in to a function defined as "def func(*a)".
Now what about this:
a, *b = e # a is 1, b is (2, 3)
That's one possible result, and presumably the one you want with
this syntax, but it's not what you'd get with the function syntax:
def func(a, *b):
Here of course you get (1, 2, 3) in "a" and () in b. To get the
same as the proposed syntax above, you can't pass in a tuple, but
have to pass the parameters separately:
func(1, 2, 3) # now a is 1, b is (2, 3)
The problem is that in function calling, you can pass in a single
tuple, which is one argument, or you can pass the elements separately
as multiple arguments, which is when the special * syntax kicks in.
When doing assignment with tuples you don't have the same two options:
a, *b = 1, 2, 3
is the same as
a, *b = (1, 2, 3)
So maybe this won't fly. Comments?
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