只有满足条件才能添加到dict [英] Only add to a dict if a condition is met

问题描述

我正在使用 urllib.urlencode 来构建Web POST参数，但是有一些值，我只想添加一个非$ > <$ code>

  apple ='green'
 orange ='orange '
 params = urllib.urlencode（{
'apple'：apple，
'orange'：orange 
}）
  pre> 
 
 
可以正常工作，但是如果我将橙色变量选为可选项，那我该如何防止它被添加参数？这样的（伪代码）：
  apple ='green'
 orange = None 
 params = urllib .urlencode（{
'apple'：apple，
 if orange：'orange'：orange 
}）
  
我希望这个很清楚，有没有人知道如何解决这个问题？
解决方案
在创建初始 dict 之后，您必须单独添加密钥：
  params = {'apple'：apple} 
如果橙色不是无：
 params ['orange'] = orange 
 params = urllib.urlencode（params）
  
 Python没有将键定义为条件的语法;你可以使用字典理解，如果你已经有一切顺序：
  params = urllib.urlencode（{k：v for k，v in（（'orange'，orange），（'apple'，apple））如果v不是无}）
  
但这不是很可读。
 
I am using urllib.urlencode to build web POST parameters, however there are a few values I only want to be added if a value other than None exists for them.
apple = 'green'
orange = 'orange'
params = urllib.urlencode({
    'apple': apple,
    'orange': orange
})
That works fine, however if I make the orange variable optional, how can I prevent it from being added to the parameters? Something like this (pseudocode):
apple = 'green'
orange = None
params = urllib.urlencode({
    'apple': apple,
    if orange: 'orange': orange
})
I hope this was clear enough, does anyone know how to solve this?
解决方案
You'll have to add the key separately, after the creating the initial dict:
params = {'apple': apple}
if orange is not None:
    params['orange'] = orange
params = urllib.urlencode(params)
Python has no syntax to define a key as conditional; you could use a dict comprehension if you already had everything in a sequence:
params = urllib.urlencode({k: v for k, v in (('orange', orange), ('apple', apple)) if v is not None})
but that's not very readable.

                        
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