def f(array): if len(array) == 1: return ''.join(array) result = list(array) i = 0 while i < len(array)-1: for j in range(2): result[i*2] = array[i] i += 1 return ''.join(result) assert f(['ac8', 'qk6', '9wg']) == 'ac8qk6qk6'
assert f(??) == 'ac8qk6qk6'
assert f(['ac8', 'qk6', '9wg']) == ??