How do I reverse an itertools.chain object?

Question

My function creates a chain of generators:

def bar(num):
    import itertools
    some_sequence = (x*1.5 for x in range(num))
    some_other_sequence = (x*2.6 fo         


        

Answer 1

if num < 0:
    lst = list(chained)
    lst.reverse()
    return lst
else:
    return chained

reversed() needs an actual sequence, because it iterates it backwards by index, and that wouldn't work for a generator (which only has the notion of "next" item).

Since you will need to unroll the whole generator anyway for reversing, the most efficient way is to read it to a list and reverse the list in-place with the .reverse() method.