Possible Duplicate:
python: most elegant way to intersperse a list with an element
Assuming I have the following list:
['a','b','c','d','e']
How can I append a new item (in this case a -) between each item in this list, so that my list will look like the following?
['a','-','b','-','c','-','d','-','e']
Thanks.
Here's a solution that I would expect to be very fast -- I believe all these operations will happen at optimized c speed.
def intersperse(lst, item):
result = [item] * (len(lst) * 2 - 1)
result[0::2] = lst
return result
Tested:
>>> l = [1, 2, 3, 4, 5]
>>> intersperse(l, '-')
[1, '-', 2, '-', 3, '-', 4, '-', 5]
The line that does all the work, result[0::2] = lst, uses extended slicing and slice assignment. The third step parameter tells python to assign values from lst to every second position in l.