Python: Merge list with range list

Question

I have a list:

L = ['a', 'b']

I need to create a new list by concatenating an original list which range goes from 1 to k. Example:

k = 4
L1 = ['a1','b1', 'a2','b2','a3','b3','a4','b4']

I try:

l1 = L * k
print l1
#['a', 'b', 'a', 'b', 'a', 'b', 'a', 'b']

l = [ [x] * 2  for x in range(1, k + 1) ]
print l
#[[1, 1], [2, 2], [3, 3], [4, 4]]

l2 = [item for sublist in l for item in sublist]
print l2
#[1, 1, 2, 2, 3, 3, 4, 4]

print zip(l1,l2)
#[('a', 1), ('b', 1), ('a', 2), ('b', 2), ('a', 3), ('b', 3), ('a', 4), ('b', 4)]

print [x+ str(y) for x,y in zip(l1,l2)] 
#['a1', 'b1', 'a2', 'b2', 'a3', 'b3', 'a4', 'b4']

But I think it is very complicated. What is the fastest and most generic solution?

Answer 1

You can use a list comprehension:

L = ['a', 'b']
k = 4
L1 = ['{}{}'.format(x, y) for y in range(1, k+1) for x in L]
print(L1)

Output

['a1', 'b1', 'a2', 'b2', 'a3', 'b3', 'a4', 'b4']