On Fri, May 10, 2013 at 5:19 PM, Jim Mooney <cybervigila...@gmail.com> wrote:
> If I'm using a variable-dependent range in a for loop, is Python smart
> enough to figure the variable once so I don't have to hoist it up?
At the start of a for loop, the interpreter gets an iterator for the
iterable. The latter is evaluated from the expression or
expression-list (tuple). If this fails it raises a TypeError.
iteration is an object protocol, using the special methods __iter__
and __next__, and the exception StopIteration. An iterator maintains
its own state. You can get an iterator manually with built-in iter()
and step through it with built-in next().
>>> it = iter('abc')
>>> type(it)
<class 'str_iterator'>
>>> next(it), next(it), next(it)
('a', 'b', 'c')
>>> next(it)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
>>> it = iter(range(5))
>>> type(it)
<class 'range_iterator'>
>>> list(it)
[0, 1, 2, 3, 4]
>>> next(it)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
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