Best way to do conditional assignment in python

I tend to use this a lot, but it's ugly:

a = (lambda x: x if x else y)(get_something())

So I wrote this function:

def either(val, alt):
    if val:
        return val
    else:
        return alt

So you can do:

a = either(get_something(), y)

Is there a built-in function for this (similar to ISNULL in T-SQL)?