How do I merge two lists into a single list?

Question

I have

a = [1, 2]
b = ['a', 'b']

I want

c = [1, 'a', 2, 'b']

Answer 1

If the order of the elements much match the order in your example then you can use a combination of zip and chain:

from itertools import chain
c = list(chain(*zip(a,b)))

If you don't care about the order of the elements in your result then there's a simpler way:

c = a + b

Answer 2

c = a + b

Need 15 characters

Answer 3

If you care about order:

#import operator
import itertools
a = [1,2]
b = ['a','b']
#c = list(reduce(operator.add,zip(a,b))) # slow.
c = list(itertools.chain.from_iterable(zip(a,b))) # better.

print c gives [1, 'a', 2, 'b']

Answer 4

[j for i in zip(a,b) for j in i]

Answer 5

Parsing

[j for i in zip(a,b) for j in i]

in your head is easy enough if you recall that the for and if clauses are done in order, followed a final append of the result:

temp = []
for i in zip(a, b):
    for j in i:
        temp.append(j)

and would be easier had it have been written with more meaningful variable names:

[item for pair in zip(a, b) for item in pair]