Python 中的迭代器 (iter()) 函数。
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Iterator (iter()) function in Python.
提问by prosseek
For dictionary, I can use iter()for iterating over keys of the dictionary.
对于字典，我可以iter()用于迭代字典的键。
y = {"x":10, "y":20}
for val in iter(y):
print val
When I have the iterator as follows,
当我有如下迭代器时，
class Counter:
def __init__(self, low, high):
self.current = low
self.high = high
def __iter__(self):
return self
def next(self):
if self.current > self.high:
raise StopIteration
else:
self.current += 1
return self.current - 1
Why can't I use it this way
为什么我不能这样使用
x = Counter(3,8)
for i in x:
print x
nor
也不
x = Counter(3,8)
for i in iter(x):
print x
but this way?
但是这样？
for c in Counter(3, 8):
print c
What's the usage of iter()function?
iter()函数的用途是什么？
ADDED
添加
I guess this can be one of the ways of how iter()is used.
我想这可能是如何iter()使用的方式之一。
class Counter:
def __init__(self, low, high):
self.current = low
self.high = high
def __iter__(self):
return self
def next(self):
if self.current > self.high:
raise StopIteration
else:
self.current += 1
return self.current - 1
class Hello:
def __iter__(self):
return Counter(10,20)
x = iter(Hello())
for i in x:
print i
采纳答案by Glenn Maynard
All of these work fine, except for a typo--you probably mean:
所有这些工作正常，除了一个错字——你可能是说：
x = Counter(3,8)
for i in x:
print i
rather than
而不是
x = Counter(3,8)
for i in x:
print x
回答by Winston Ewert
I think your actual problem is that you print xwhen you mean to print i
我认为你的实际问题是print x当你想print i
iter()is used to obtain an iterator over a given object. If you have an __iter__method that defines what iter will actually do. In your case you can only iterate over the counter once. If you defined __iter__to return a new object it would make it so that you could iterate as many times as you wanted. In your case, Counter is already an iterator which is why it makes sense to return itself.
iter()用于获取给定对象的迭代器。如果您有一个__iter__方法来定义 iter 将实际执行的操作。在您的情况下，您只能在计数器上迭代一次。如果您定义__iter__返回一个新对象，它将使它可以根据需要进行多次迭代。在您的情况下， Counter 已经是一个迭代器，这就是为什么返回自身是有意义的。
