Python:for 循环 - for i in range(0,len(list) vs for i in list

Question

这是一个非常简单的 Python 力学问题。为什么我不能只说 for i in range original_list 而不是 for i in range(0, len(original_list))。人们通常使用前者的范围吗？谢谢!

# "If I give you an array with negative and positive numbers (i.e. {3,2,-3,6,4,-7}) and asked you to sort it so that the negative numbers appeared first but you didn't change the relative order of the remaining numbers, how would you do it? (i.e. the final result would be {-3,-7,3,2,6,4}).

original_list = [3, 2, -3, 6, 4, -7]
pos_list = []
neg_list = []

for i in range(0, len(original_list)):
    if original_list[i] < 0:
        neg_list.append(original_list[i])
    else:
        pos_list.append(original_list[i])

print neg_list + pos_list

Answer 1

在您的情况下，由于您不需要使用列表中项目的索引，您可以使用 for in 对其进行迭代:

>>> for item in original_list:
...     if item < 0:
...         ...

如果您想遍历列表中项目的索引，请使用for in range(..):

>>> for i in range(len(original_list)):
...     if original_list[i] < 0:
...         ...

或者，您可能还想使用 enumerate()如果您需要循环体中的项目和索引:

>>> for i, item in enumerate(original_list):
...    if item < 0:
...        ...

通过这种方式，您还可以消除 original_list[i] 的使用。