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?
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.
If you are using Python 3.9 or newer, you could use the new dict merging operator support and a conditional expression:
params = urllib.urlencode(
{'apple': apple} |
({'orange': orange} if orange is not None else {})
)
but I find readability suffers, and so would probably still use a separate if expression:
params = {'apple': apple}
if orange is not None:
params |= {'orange': orange}
params = urllib.urlencode(params)
Another option is to use dictionary unpacking, but for a single key that's not all that more readable:
params = urllib.urlencode({
'apple': apple,
**({'orange': orange} if orange is not None else {})
})
I personally would never use this, it's too hacky and is not nearly as explicit and clear as using a separate if statement. As the Zen of Python states: Readability counts.