On Tue, Nov 11, 2014 at 4:52 AM, Alan Gauld <alan.ga...@btinternet.com> wrote:
> On 11/11/14 04:45, Clayton Kirkwood wrote:
>
>>>> *list(range(1,6))
>>
>> File "<input>", line 1
>> SyntaxError: can use starred expression only as assignment target
>
> list() is a function. You cannot unpack a function.
>
> Also the * operator needs to be used inside a function parameter list.
> (There may be some obscure case where you can use it outside of that but 99%
> of the time that's the only place you'll see it used.)
Python 3 extended unpacking:
>>> a, *bcd, e = 'abcde'
>>> a
'a'
>>> bcd
['b', 'c', 'd']
>>> e
'e'
>>> for x, *rest in ('abc', 'de'):
... print(x, rest)
...
a ['b', 'c']
d ['e']
>>>>> a = list(range(*5))
>
> And here 5 is an integer. It must be a sequence.
Any iterable suffices.
Refer to the table in section 8.4.1 for an overview of container interfaces:
http://docs.python.org/3/library/collections.abc
A common non-sequence example is unpacking a generator:
>>> gen = (c.upper() for c in 'abcde')
>>> print(*gen, sep='-')
A-B-C-D-E
A generator is an iterable:
>>> gen = (c.upper() for c in 'abcde')
>>> type(gen)
<class 'generator'>
>>> hasattr(gen, '__iter__')
True
>>> isinstance(gen, collections.Iterable)
True
and also an iterator:
>>> hasattr(gen, '__next__')
True
>>> isinstance(gen, collections.Iterator)
True
>>> it = iter(gen)
>>> it is gen
True
>>> next(it), next(it), next(it), next(it), next(it)
('A', 'B', 'C', 'D', 'E')
>>> next(it)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
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