Only add to a dict if a condition is met

Question

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

Answer 1

I really like the neat trick in the answer here: https://stackoverflow.com/a/50311983/3124256

But, it has some pitfalls:

1. Duplicate if tests (repeated for key and value)
2. Pesky None: None entry in the resulting dict

To avoid this, you can do the following:

apple = 23
orange = None
banana = None
a = {
    'apple' if apple else None: apple,
    'orange' if orange else None : orange,
    'banana' if banana else None: banana,
    None: None,
}
del a[None]

Expected Output : {'apple': 23}

Note: the None: None entry ensures two things:

1. The None key will always be present (del won't throw an error)
2. The contents of 'None values' will never exist in the dict (in case you forget to del afterwards)

If you aren't worried about these things, you can leave it out and wrap the del in a try...except (or check if the None key is present before deling). To address number 2 alternatively, you could also put the conditional check on the value (in addition to the key).