#

# File: binary_search.py

# ----------------------------

# The binary_search function takes a sorted array and an item.

# If the item is in the array, the function returns its position.

#

def binary_search( list , item):

low = 0

high = len (list) - 1

while low <= high : # While you haven't narrowed it down to one element

mid = (low + high) # Check the middle element

guess = list [mid]

if guess == item : # Found the item

return mid

if guess > item : # The guess was too high

high = mid - 1

else: # The guess was too low

low = mid + 1

return None # The item doesn't exist

my_list = [ 1 ,3, 5, 7, 9 ]

print binary_search(my_list, 3)

print binary_search(my_list, -1)