Most pythonic way to get the previous element

Question

I would like an enumerate-like functional on iterators which yields the pair (previous_element, current_element). That is, given that iter

Answer 1

def offset(iter, n=1, pad=None):
    i1, i2 = itertools.tee(iter)
    i1_padded = itertools.chain(itertools.repeat(pad, n), i1)
    return itertools.izip(i1_padded, i2)

@bpgergo + @user792036 = this. Best of two worlds :).