Joining pairs of elements of a list

You can use slice notation with steps:

>>> x = "abcdefghijklm">>> x[0::2] #0. 2. 4...'acegikm'>>> x[1::2] #1. 3. 5 ..'bdfhjl'>>> [i+j for i,j in zip(x[::2], x[1::2])] # zip makes (0,1),(2,3) ...['ab', 'cd', 'ef', 'gh', 'ij', 'kl']

Same logic applies for lists too. String lenght doesn't matter, because you're simply adding two strings together.

Use an iterator.

List comprehension:

>>> si = iter(['abcd', 'e', 'fg', 'hijklmn', 'opq', 'r'])>>> [c+next(si, '') for c in si]['abcde', 'fghijklmn', 'opqr']

• Very efficient for memory usage.
• Exactly one traversal of s

Generator expression:

>>> si = iter(['abcd', 'e', 'fg', 'hijklmn', 'opq', 'r'])>>> pair_iter = (c+next(si, '') for c in si)>>> pair_iter # can be used in a for loop<generator object at 0x4ccaa8>>>> list(pair_iter) ['abcde', 'fghijklmn', 'opqr']

• use as an iterator

Using map, str.__add__, iter

>>> si = iter(['abcd', 'e', 'fg', 'hijklmn', 'opq', 'r'])>>> map(str.__add__, si, si)['abcde', 'fghijklmn', 'opqr']

next(iterator[, default]) is available starting in Python 2.6

just to be pythonic :-)

>>> x = ['a1sd','23df','aaa','ccc','rrrr', 'ssss', 'e', '']>>> [x[i] + x[i+1] for i in range(0,len(x),2)]['a1sd23df', 'aaaccc', 'rrrrssss', 'e']

in case the you want to be alarmed if the list length is odd you can try:

[x[i] + x[i+1] if not len(x) %2 else 'odd index' for i in range(0,len(x),2)]

Best of Luck