which is "better" (or more Pythonic)?

[Skaperen]

i have a little function that i am considering whether or not i should use a variable for some intermediate data:

form 1:

    ...
    with Popen(cmd,stdout=PIPE,universal_newlines=all(isinstance(x,str)for x in cmd)) as p:
        return p.stdout.read().splitlines()

or

form 2:

    ...
    un = all(isinstance(x,str)for x in cmd))
    with Popen(cmd,stdout=PIPE,universal_newlines=un) as p:
        return p.stdout.read().splitlines()

should i use the extra variable or not? i'm sure it would slow things down a minuscule undetectable amount.

i did indent the above code by 4 more spaces than it shows in the preview.