我有一个相当简单的循环
cities = ['Merano', 'Madrid', 'New York', 'Bangkok']
countries = ['Italy', 'Spain', 'USA']
for index, city in enumerate(cities):
print('This is index:', index)
print('This is city:', city)
print('The length of the list 'cities' is: ', len(cities))
print(print('The length of the list 'countries' is: ', len(countries)))
print(countries[index])
print(5 * '#')
我希望它能坏掉。然而，我没有想到的是这个输出。
This is index: 0
This is city: Merano
The length of the list 'cities' is: 4
The length of the list 'countries' is: 3
None
Italy
#####
This is index: 1
This is city: Madrid
The length of the list 'cities' is: 4
The length of the list 'countries' is: 3
None
Spain
....
none从哪里来？我不print这个，也不执行我希望打印的东西。。。
您在print(print('The length of the list 'countries' is: ', len(countries)))中使用了print(print(使用
print('The length of the list 'countries' is: ', len(countries))`
因为您有两个打印命令
print(print('The length of the list 'countries' is: ', len(countries)))
print(print('The length of the list 'countries' is: ', len(countries)))
在上面的行中，您正在打印打印功能输出。
如果您查看函数Def，它没有返回类型，因此您从内部print()语句中获得None。
还有备注-修复index > len(countries)的index检查