zefciu schrieb: > In the tutorial there is an example iterator class that revesrses the > string given to the constructor. The problem is that this class works > only once, unlike built-in types like string. How to modify it that it > could work several times? I have tried two approaches. They both work, > but which of them is stylistically better? > > class Reverse: #original one > "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] > > class Reverse: #1st approach > "Reuseable 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: > self.index = len(self.data) #Reset when previous > # > iterator goes out > raise StopIteration > self.index = self.index - 1 > return self.data[self.index] > > class Reverse: #2nd approach > "Reuseable Iterator for looping over a sequence backwards" > def __init__(self, data): > self.data = data > def __iter__(self): > self.index = len(self.data) #Reset as a part of iterator > # creation > return self > def next(self): > if self.index == 0: > raise StopIteration > self.index = self.index - 1 > return self.data[self.index]
None. You don't reuse iterators! In the actualy example, reusage is possible due to the whole data being known & available. But there might be cases where this isn't possible - e.g. fetching data from a remote location which is too large to fit into memory for re-iteration. So generally speakiing, if you need an iterator, construct it. Regards, Diez -- http://mail.python.org/mailman/listinfo/python-list
