Anders Kaseorg <ande...@mit.edu> added the comment:
As an experienced Python programmer I am obviously aware that the tutorial is
trying to teach how to make an iterator class, not how to make a container
class.
But the tutorial doesn’t make that *clear*. It should be much more explicit
about what it is explaining to avoid confusing those concepts in the minds of
beginners. (Or even the staff of the MIT introductory CS course.)
One way to fix this confusion would be to explain what one should do for both
container classes and iterator classes:
"""
Having seen the mechanics behind the iterator protocol, it is easy to add
iterator behavior to your container classes. Define a :meth:`__iter__` method
which returns an object of a separate iterator class. The iterator class
should have a :meth:`next` method and an :meth:`__iter__` method (the
:meth:`__iter__` method of the iterator class should just return ``self``)::
class ReverseList(object):
"Container that lets you iterate over the items backwards"
def __init__(self, data):
self.data = data
def __iter__(self):
return ReverseIterator(self.data)
class ReverseIterator(object):
"Iterator for looping over a sequence backwards"
def __init__(self, data):
self.data = data
self.index = len(data)
def __iter__(self):
return self
def next(self):
if self.index == 0:
raise StopIteration
self.index = self.index - 1
return self.data[self.index]
>>> for char in ReverseIterator('spam'):
... print char
...
m
a
p
s
>>> for char in ReverseList([1,2,3]):
... print char
...
3
2
1
"""
----------
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue8376>
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