Python list comprehension - simple

Question

I have a list and I want to use a certain function only on those entries of it that fulfills a certain condition - leaving the other entries unmodified.

Example: Say

Answer 1

a_list = [1, 2, 3, 4, 5]

print [elem*2 if elem%2==0 else elem  for elem in a_list ]  

or, if you have a very long list that you want to modify in place:

a_list = [1, 2, 3, 4, 5]

for i,elem in enumerate(a_list):
    if elem%2==0:
        a_list[i] = elem*2

so, only the even elements are modified