Suppose I have this code:
def f(x): return 2*x,x*x x = range(3) xlist, ylist = [f(value) for value in x]
How can I neatly get a result like this?
xlist = [0, 2, 4] ylist = [0, 1, 4]
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Answer
Note that return 2*x,x
is short for return (2*x,x)
, i.e. a tuple. Your list comprehension thus generates a list of tuples, not a tuple of lists. The nice thing of zip
however is that you can easily use it in reverse with the asterisk:
xlist,ylist = zip(*[f(value) for value in x]) # ^ with asterisk
Note that xlist
and ylist
will be tuples (since zip
will be unpacked). If you want them to be lists, you can for instance use:
xlist,ylist = map(list, zip(*[f(value) for value in x]))
which results in:
>>> xlist [0, 2, 4] >>> ylist [0, 1, 4]
Another way to do this is with separate list comprehensions:
xlist = [f(value)[0] for value in x] ylist = [f(value)[1] for value in x]
Of course, this repeats the work of f
, which is inelegant and can be inefficient.