Joining pairs of elements of a list

Question

I know that a list can be joined to make one long string as in:

x = [\'a\', \'b\', \'c\', \'d\']
print \'\'.join(x)

Obviously this would ou

Answer 1

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

>>> 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