# [Tutor] Binary chop function - this works, but I'm not sure why

Arun Srinivasan soulguidedtelescope at gmail.com
Thu Feb 14 01:49:47 CET 2008

```I'm trying to learn Python, and I decided to try kata 2 </> from the
CodeKate website. It's basically just a challenge to implement a binary
search in different ways.

I wrote an implementation that works, but I'm confused as to why.

def chop(search_int, sorted_list):
if len(sorted_list) == 1 or 2:
for x in sorted_list:
if x == search_int:
return sorted_list.index(x)
return -1

midpoint = (len(sorted_list) - 1) / 2
mp_value = sorted_list[midpoint]

if mp_value == search_int:
return midpoint
elif mp_value > search_int:
return chop(search_int, sorted_list[:midpoint])
else:
return chop(search_int, sorted_list[midpoint + 1:])

Basically, it only returns the index if it matches in the if statement at
the beginning of the function, but since that is limited to lists of length
2 or 1, why doesn't it return only 0 or 1 as the index? I think there is
something about recursion here that I'm not fully comprehending.
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