遍历一个可迭代对象中的所有元素，但是却不想使用for循环

def manual_iter():
    with open('/etc/passwd') as f:
        try:
            while True:
                line = next(f)
                print(line, end='')
        except StopIteration:
            pass

or

with open('/etc/passwd') as f:
    while True:
        line = next(f, None)
        if line is None:
            break
        print(line, end='')

下面的交互示例向我们演示了迭代期间所发生的基本细节：

>>> items = [1, 2, 3]
>>> # Get the iterator
>>> it = iter(items) # Invokes items.__iter__()
>>> # Run the iterator
>>> next(it) # Invokes it.__next__()
1
>>> next(it)
2
>>> next(it)
3
>>> next(it)
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
StopIteration
>>>