Python lambda call function with None output

Question

I want to realize something like use lambda to call a function which has an output of None or list and if it is a list, then get the first value.

lambda x: func(x,args)[0] if func(x,args) is not None else None

However, in this function it seems to need to call the function twice to find out whether it is None. Of course I can just write the code using try or conditional statements:

def function(x):
    try: 
        return func(x,args)[0]
    except (IndexError,TypeError):
        return None

or just change the output of func. But I am still curious about if there are some methods to call the function only once with lambda.

At the very least only catch the IndexError and TypeError exceptions that your code can throw, not everything else (including memory errors and keyboard interrupts). — Martijn Pieters
– Martijn Pieters, Commented Jul 11, 2017 at 12:46
Why not list = func(x,args); lambda x: list[0] if list else None — yinnonsanders
– yinnonsanders, Commented Jul 11, 2017 at 12:49

deceze · Accepted Answer · 2017-07-11 12:45:47Z

14

This'll do:

lambda x: (func(x, args) or [None])[0]

answered Jul 11, 2017 at 12:45

deceze♦

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