["python","variables","dictionary","urllib"]
Only add to a dict if a condition is met

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.