[Python-ideas] Why does `sum` use a default for the `start` parameter?
algorias at gmail.com
Sat Dec 5 19:55:53 CET 2009
2009/12/5 Ram Rachum <cool-rr at cool-rr.com>:
> MRAB <python at ...> writes:
>> > I prefer (b). The problem with requiring `start` for sequences of non-
>> > objects is that you now have to go out and create a "zero object" of the
>> > type as your other objects. The object class might not even have a concept
> of a
>> > "zero object".
>> If the objects can be summed, shouldn't there also be a zero object?
>> Does anyone have an example when that's not possible?
> You're right MRAB, probably almost every object type that has a concept of
> "addition" will have a concept of a zero element.
> BUT, that zero object has to be created by the user of `sum`, and that has two
> 1. The user might not know from beforehand which type of object he's adding.
> Even within the same type there might be problems. What happens when the user is
> using `sum` to add a bunch of vectors, and he doesn't know from beforehand what
> the dimensions of the vectors are? How will he know if his zero element should
> be Vector([0, 0]) or Vector([0, 0, 0])
Ugly, but works:
itr = iter(sequence)
This is actually a good example in favor of not requiring a start value.
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