f---ing typechecking

[Neil Cerutti]

On 2007-02-14, Farshid Lashkari <no at spam.com> wrote:
> Szabolcs Nagy wrote:
>>>>> L=[1]
>>>>> L.extend((1,))
>>>>> L
>> [1, 1]
>
> Are list.extend() and list concatenation supposed to behave
> differently? I always thought concatenation was just shorthand
> for calling extend().

They are different. list.extend() mutates the list, returning
None, while the + operator returns a new, concatenated list.

+= on the other hand works very similarly to list.extend().
However:

>>> [1, 2].extend([3])
>>> [1, 2] += [3]
SyntaxError: augmented assign to list literal or comprehension not possible

> It seems like the '+' operator for lists should accept any
> iterable for the right side argument to be consistent with
> extend() and the '+=' operator.

+= will only perform the operation in place "whenever possible",
so there are objects for which a conversion to .extend wouldn't
work, and you'd get an actual call of the + operation followed by
the assignment operation.

-- 
Neil Cerutti
I don't know what to expect right now, but we as players have to do what we've
got to do to make sure that the pot is spread equally. --Jim Jackson