Add an item between each item already in the list [duplicate]

Answer 1

The following will add a "separator" element between each of those in a list:

seq = ['a','b','c','d','e']

def tween(seq, sep):
    return reduce(lambda r,v: r+[sep,v], seq[1:], seq[:1])

print tween(seq, '-')

output:

['a', '-', 'b', '-', 'c', '-', 'd', '-', 'e']

FWIW, here's a similar thread titled Custom string joining in the Usenet comp.lang.python group that might interest you.