Question

people = ['mago','pipa','john','mat']
>>> for people in people:
    print(people)


mago
pipa
john
mat
>>> for people in people:
    print(people)


m
a
t
>>> for people in people:
    print(people)


t
>>> for people in people:
    print(people)


t
>>> for people in people:
    print(people)


t
>>> for people in people:
    print(people)

Answer 1

for循环不会为索引创建新范围;您使用循环索引people覆盖列表people。

for循环几乎是以下代码的语法糖：

# for people in people:   # iter() is called implicitly on the iterable
#    print(people)
people_itr = iter(people)
while True:
    try:
        people = next(people_itr)
    except StopIteration:
        break
    print(people)
del people_itr

因此，尽管您引用了people最初引用的列表，但名称 people会不断更新，以引用一个元素那份清单。当您运行第二个循环时，people现在是对列表中 last 字符串的引用。第三个和后续循环代表一个固定点;字符串上的迭代器返回连续的1个字符的字符串，因此您可以快速到达字符串是其唯一元素的点。

在您的示例中，people在第一个循环后绑定到"mat"，而不是您的列表。在第二个（以及第三个和第四个）循环之后，people绑定到"t"。

您可以通过将来电链接到__getitem__（即[-1]）来看到同样的事情：

>>> people[-1]
'mat'
>>> people[-1][-1]
't'
>>> people[-1][-1][-1]
't'
>>> people[-1][-1][-1][-1]
't'

这里发生了什么？与人们在人们打印人循环

1 个答案: