Python：检查‘Dictionary‘是否为空似乎不起作用

本文翻译自：Python: Checking if a 'Dictionary' is empty doesn't seem to work

I am trying to check if a dictionary is empty but it doesn't behave properly. 我正在尝试检查字典是否为空但它的行为不正常。 It just skips it and displays ONLINE without anything except of display the message. 除了显示消息之外，它只是跳过它并显示ONLINE而没有任何内容。 Any ideas why ? 有什么想法吗？

 def isEmpty(self, dictionary):
   for element in dictionary:
     if element:
       return True
     return False

 def onMessage(self, socket, message):
  if self.isEmpty(self.users) == False:
     socket.send("Nobody is online, please use REGISTER command" \
                 " in order to register into the server")
  else:
     socket.send("ONLINE " + ' ' .join(self.users.keys())) 

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#1楼

参考：https://stackoom.com/question/1ZFVf/Python-检查-Dictionary-是否为空似乎不起作用

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#2楼

Empty dictionaries evaluate to False in Python: Python中的空字典评估为False ：

>>> dct = {}
>>> bool(dct)
False
>>> not dct
True
>>>

Thus, your isEmpty function is unnecessary. 因此，您的isEmpty函数是不必要的。 All you need to do is: 你需要做的就是：

def onMessage(self, socket, message):
    if not self.users:
        socket.send("Nobody is online, please use REGISTER command" \
                    " in order to register into the server")
    else:
        socket.send("ONLINE " + ' ' .join(self.users.keys()))

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#3楼

Here are three ways you can check if dict is empty. 以下三种方法可以检查dict是否为空。 I prefer using the first way only though. 我更喜欢使用第一种方式。 The other two ways are way too wordy. 另外两种方式太过于罗嗦。

test_dict = {}

if not test_dict:
    print "Dict is Empty"


if not bool(test_dict):
    print "Dict is Empty"


if len(test_dict) == 0:
    print "Dict is Empty"

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#4楼

use 'any' 使用'任何'

dict = {}

if any(dict) :

     # true
     # dictionary is not empty 

else :

     # false 
     # dictionary is empty

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#5楼

Why not use equality test? 为什么不使用平等测试？

def is_empty(my_dict):
    """
    Print true if given dictionary is empty
    """
    if my_dict == {}:
        print("Dict is empty !")

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#6楼

dict = {}
print(len(dict.keys()))

if length is zero means that dict is empty 如果length为零则表示dict为空