python - 多个for循环，不满足条件只打印一次else

Question

循环中有一个循环，如果满足条件则运行一些代码。但是，如果不满足条件，我需要它来打印一些东西。虽然如果我将代码添加到任何位置，它会被打印多次。如果不满足条件，如何让它只打印一次？

some_list = {'a_list': [{'name': 'Tom', 'age': 25}, {'name': 'John', 'age': 25}, {'name': 'Val', 'age': 25}], 'b_list': [{'name': 'Don', 'age': 25}, {'name': 'Tim', 'age': 25}, {'name': 'San', 'age': 25}]}

findperson = 'San'

for i in some_list:
    for y in some_list[i]:
        if y['name'].lower() == findperson.lower():
            print('Friend found')
            break
else:            
    print('Friend not found')

Answer 1

您可以对内部循环使用any(并在外部循环中使用break)...

for i in some_list:
    if any(y['name'].lower() == findperson.lower() for y in some_list[i]):
        print('Friend found')
        break
else:            
    print('Friend not found')

...甚至整个事情:

if any(y['name'].lower() == findperson.lower() 
       for i in some_list for y in some_list[i]):
    print('Friend found')
else:            
    print('Friend not found')

如果你还需要实际的 friend ，你可以使用next:

for i in some_list:
    friend = next((y for y in some_list[i] if y['name'].lower() == findperson.lower()), None)
    if friend is not None:
        print('Friend found:', friend)
        break
else:            
    print('Friend not found')

也适用于嵌套生成器，如上面的any:

friend = next((y for i in some_list for y in some_list[i] 
                 if y['name'].lower() == findperson.lower()),
              None)
if friend is not None:
    print('Friend found:', friend)
else:            
    print('Friend not found')