def before_after(string, start = 0):
source = peekable(iter(string.split("\n")))
before = 0
after = 0
for line in shift_iter(source, start): before += 1
for line in source: after += 1
return (before, after)
def shift(source, depth = tab_length):
initial = 0
start = 0
source = peekable(lines(source))
result = "\n".join(shift_iter(source, initial, start, tab_length, depth))
return result
