The best way to think of it is that .split() is like .split(' '), except that it's splitting on any whitespace character instead of just ' ', and keepempty is defaulting to False instead of True.

Therefore:

    '   x y z'.split(maxsplit=1, keepempty=True) == ['', '  x y z']

because:

    '   x y z'.split(' ', maxsplit=1) == ['', '  x y z']

but:

    '   x y z'.split(maxsplit=1, keepempty=False) == ['x y z']

At least, I think that's the case!