> You could do what mathematicians do when they deal with alternating > signs: they raise -1 to the power of the index to get an appropriate > multiplier. > > >>> [ n * (-1) ** n for n in range(10) ] > [0, -1, 2, -3, 4, -5, 6, -7, 8, -9] > >>> > > Or you could do here what you attempt to do with map below. See below. >
> > You are trying to use a binary expression. There are no binary > expressions. Add an else branch to make it ternary: > > lambda x : x if x % 2 == 0 else -x > > But never mind the number of branches, the serious point is that you > didn't specify a value for when the condition is not true. It doesn't > make sense without that. > > There's nothing wrong with a list comprehension, or the corresponding > generator expression if you want a generator. It's fine. Map's fine. Thanks Jussi I really like the multiplier solution. -- https://mail.python.org/mailman/listinfo/python-list
