@@ -1,30 +1,77 @@
-def binarySearch(alist, item):
-
-first = 0
-last = len(alist)-1
-found = False
-
-while first<=last and not found:
-
-midpoint = (first + last)//2
-if alist[midpoint] == item:
-found = True
-print("Found [ at position: %s ]" % (alist.index(item) + 1))
+"""
+This is pure python implementation of binary search algorithm
+
+For doctests run following command:
+python -m doctest -v selection_sort.py
+or
+python3 -m doctest -v selection_sort.py
+
+For manual testing run:
+python binary_search.py
+"""
+from __future__ import print_function
+
+
+def binary_search(sorted_collection, item):
+"""Pure implementation of binary sort algorithm in Python
+
+:param sorted_collection: some sorted collection with comparable items
+:param item: item value to search
+:return: index of found item or None if item is not found
+
+Examples:
+>>> binary_search([0, 5, 7, 10, 15], 0)
+0
+
+>>> binary_search([0, 5, 7, 10, 15], 15)
+4
+
+>>> binary_search([0, 5, 7, 10, 15], 5)
+1
+
+>>> binary_search([0, 5, 7, 10, 15], 6)
+
+>>> binary_search([5, 2, 1, 5], 2)
+Traceback (most recent call last):
+...
+ValueError: Collection must be sorted
+"""
+if sorted_collection != sorted(sorted_collection):
+raise ValueError('Collection must be sorted')
+left = 0
+right = len(sorted_collection) - 1
+
+while left <= right:
+midpoint = (left + right) // 2
+current_item = sorted_collection[midpoint]
+if current_item == item:
+return midpoint
 else:
-
-if item < alist[midpoint]:
-
-last = midpoint-1
+if item < current_item:
+right = midpoint - 1
 else:
-first = midpoint+1
-
-if found == False:
-continue
-# print("Not found")
-return found
-print("Enter numbers seprated by space")
-s = input()
-numbers = list(map(int, s.split()))
-trgt =int( input('enter a single number to be found in the list '))
-binarySearch(numbers, trgt)
+left = midpoint + 1
+return None
+
+
+if __name__ == '__main__':
+import sys
+# For python 2.x and 3.x compatibility: 3.x has not raw_input builtin
+# otherwise 2.x's input builtin function is too "smart"
+if sys.version_info.major < 3:
+input_function = raw_input
+else:
+input_function = input
+
+user_input = input_function('Enter numbers separated by coma:\n')
+collection = [int(item) for item in user_input.split(',')]
 
+target_input = input_function(
+'Enter a single number to be found in the list:\n'
+)
+target = int(target_input)
+result = binary_search(collection, target)
+if result is not None:
+print('{} found at positions: {}'.format(target, result))
+else:
+print('Not found')