Python for循环是基于迭代器的“ for-each”循环。每次迭代开始时都会重新分配迭代变量。换句话说，以下循环：
In [15]: nums = 1,2,5,8
In [16]: for num in nums:
...: print(num)
...:
1
2
5
8
等效于：
In [17]: it = iter(nums)
...: while True:
...: try:
...: num = next(it)
...: except StopIteration:
...: break
...: print(num)
...:
1
2
5
8
同样，以下循环是等效的：
In [19]: for num in nums:
...: print("num:", num)
...: num += 1
...: print("num + 1:", num)
...:
...:
num: 1
num + 1: 2
num: 2
num + 1: 3
num: 5
num + 1: 6
num: 8
num + 1: 9
In [20]: it = iter(nums)
...: while True:
...: try:
...: num = next(it)
...: except StopIteration:
...: break
...: print("num:", num)
...: num += 1
...: print("num + 1:", num)
...:
num: 1
num + 1: 2
num: 2
num + 1: 3
num: 5
num + 1: 6
num: 8
num + 1: 9
请注意，C样式的for循环在Python中不存在，但是您始终可以编写while循环（c样式的for循环本质上是while循环的语法糖）：
for(int i = 0; i < n; i++){
// do stuff
}
等效于：
i = 0
while i < n:
# do stuff
i += 1
请注意，不同之处在于，在这种情况下，迭代 取决于i# do stuff，修改的任何内容i都会影响迭代，而在前一种情况下，迭代取决于迭代器 。注意，如果我们确实修改了迭代器，则迭代会受到影响：
In [25]: it = iter(nums) # give us an iterator
...: for num in it:
...: print(num)
...: junk = next(it) # modifying the iterator by taking next value
...:
...:
1
5
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