python - 如何检查具有列表或字典的元组是否为空

Question

我有一个元组:

details = ({}, [])

由于以下元组中没有数据，我想返回一个空响应。为此，我正在写:

 if not details:
      return Response({})
 else:
    print "Not null"

但这似乎不起作用，因为它总是在 else 部分进行并且打印不为空。我是 python 的新手。感谢您的帮助。

Answer 1

Note: if you write:

if <expr>:
    pass

then Python will not check that <expr> == True, it will evaluate the truthiness of the <expr>. Objects have some sort of defined "truthiness" value. The truthiness of True and False are respectively True and False. For None, the truthiness is False, for numbers usually the truthiness is True if and only if the number is different from zero, for collections (tuples, sets, dictionaries, lists, etc.), the truthiness is True if the collection contains at least one element. By default custom classes have always True as truthiness, but by overriding the __bool__ (or __len__), one can define custom rules.

元组的真实性是True给定元组本身包含一个或多个项目(否则为 False)。这些元素是什么无关紧要。

如果您想检查至少元组中的一项具有真实性 True , 我们可以使用 any(..) :

if not <b>any(</b>details<b>)</b>:  # all items are empty
    return Response({})
else:
    print "Not null"

因此从列表包含至少一个元素或字典或两者的那一刻起，else案例将被触发，否则 if body 会着火。

如果我们想检查元组中的所有元素是否真实True , 我们可以使用 all(..) :

if not <b>all(</b>details<b>)</b>:  # one or more items are empty
    return Response({})
else:
    print "Not null"