CODEWITHSUNDEEP
python
Forna
Forna

Reputation: 111

Check multiple variables for None and assign the first variable that is not None

Is there a way to improve this code to make it shorter?

if date_a is None and date_b is None and date_c is None: 
    start_date = current_date
else:
    if date_a is not None:
        start_date = date_a
    elif date_b is not None:
        start_date = date_b
    elif date_c is not None:
        start_date = date_c

Upvotes: 1

Views: 2471

Answers (4)

Marco Bonelli
Marco Bonelli

Reputation: 69276

As an alternative in Python >= 3.8 you can use an assignment expression plus any():

any(start_date := d for d in (date_a, date_b, date_c, current_date))

In your specific case I suspect that a chain of or would be faster, however any() will also work well if you have a collection of variables and not just single variables with different names:

any(start_date := d for d in dates)

The return value of any will let you know whether there was some truthy value or not.

Upvotes: 2

Pi Marillion
Pi Marillion

Reputation: 4674

First, you can remove one if/else depth:

if date_a is not None:
    start_date = date_a
elif date_b is not None:
    start_date = date_b
elif date_c is not None:
    start_date = date_c
else:
    start_date = current_date

You could also take advantage of the for...else statement:

for start_date in (date_a, date_b, date_c):
    if start_date is not None:
        break
else:
    start_date = current_date

The else only happens if none of the break conditions triggered, e.g. if all of the potential start_date's were None.

Upvotes: 1

juanpa.arrivillaga
juanpa.arrivillaga

Reputation: 95908

You can do something like:

start_date = date_a or date_b or date_c or current_date

Alternatively, there really is nothing wrong with:

if date_a is not None:
    start_date = date_a
elif date_b is not None:
    start_date = date_b
elif date_c is not None:
    start_date = date_c
else:
    start_date = current_date

Upvotes: 0

Samwise
Samwise

Reputation: 71444

You can use or, which will give you the first truthy value:

start_date = date_a or date_b or date_c or current_date

Another solution would be to turn them into an iterable, add an is None filter, and pull the first item using next():

start_date = next(date for date in (
    date_a, 
    date_b, 
    date_c, 
    current_date
) if date is not None)

This approach works better if you need a condition other than "truthiness", or if you have a lot of values (in which case organizing them in an iterable container is likely easier than pasting them into a long or sequence).

Upvotes: 2

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