I've been learning about how to implement an iterator in a class from Core Python Programming (2nd Edition).
>>> class AnyIter(object):
... def __init__(self, data, safe=False):
... self.safe = safe
... self.iter = iter(data)
...
... def __iter__(self):
... return self
...
... def next(self, howmany=1):
... retval = []
... for eachItem in range(howmany):
... try:
... retval.append(self.iter.next())
... except StopIteration:
... if self.safe:
... break
... else:
... raise
... return retval
...
>>>
>>> a = AnyIter(range(10))
>>> i = iter(a)
>>> for j in range(1,5):
... print j, ':', i.next(j)
...
1 : [0]
2 : [1, 2]
3 : [3, 4, 5]
4 : [6, 7, 8, 9]
I am confused by this statement:
>>> i = iter(a)
Why do I need to turn 'a' into an iterator? Didn't I already do this when I constructed the class?
As a test, I tried the following:
>>> for j in range(1,5):
... print j, ':', a.next(j)
...
1 :
Traceback (most recent call last):
File "<stdin>", line 2, in ?
File "<stdin>", line 13, in next
StopIteration
>>>
Why didn't that work?