python中判断列表元素是否为空

 

1、

>>> a = []
>>> b = ["aa","bb","cc"]
>>> if len(a) == 0:
    print("empty!")

    
empty!
>>> if len(b) == 0:
    print("empty!")

    

 

2、

>>> a = ["aa","bb","cc","dd"]
>>> for i in a:
    print(i)
else:
    print("empty!")

    
aa
bb
cc
dd
empty!
>>> if a:   ## 需要加if a
    for i in a:
        print(i)
else:
    print("empty!")

    
aa
bb
cc
dd

>>> a = []
>>> for i in a:
    print(i)
else:
    print("empty!")

    
empty!
>>> if a:    ## 正确
    for i in a:
        print(i)
else:
    print("empty!")

    
empty!

 

3、

>>> a = ["aa","bb","cc","dd"]
>>> if len(a) != 0:
    for i in a:
        print(i)
else:
    print("empty!")

    
aa
bb
cc
dd
>>> a = []
>>> if len(a) != 0:
    for i in a:
        print(i)
else:
    print("empty!")

    
empty!