new_contents: """
  This is pure python implementation of sentinel linear search algorithm
  
  For doctests run following command:
  python -m doctest -v sentinel_linear_search.py
  or
  python3 -m doctest -v sentinel_linear_search.py
  
  For manual testing run:
  python sentinel_linear_search.py
  """
  
  def sentinel_linear_search(sequence, target):
      """Pure implementation of sentinel linear search algorithm in Python
  
      :param sequence: some sequence with comparable items
      :param target: item value to search
      :return: index of found item or None if item is not found
  
      Examples:
      >>> sentinel_linear_search([0, 5, 7, 10, 15], 0)
      0
  
      >>> sentinel_linear_search([0, 5, 7, 10, 15], 15)
      4
  
      >>> sentinel_linear_search([0, 5, 7, 10, 15], 5)
      1
  
      >>> sentinel_linear_search([0, 5, 7, 10, 15], 6)
  
      """
      sequence.append(target)
  
      index = 0
      while sequence[index] != target:
          index += 1
  
      sequence.pop()
  
      if index == len(sequence):
          return None
  
      return index
  
  
  if __name__ == '__main__':
      try:
          raw_input          # Python 2
      except NameError:
          raw_input = input  # Python 3
  
      user_input = raw_input('Enter numbers separated by comma:\n').strip()
      sequence = [int(item) for item in user_input.split(',')]
  
      target_input = raw_input('Enter a single number to be found in the list:\n')
      target = int(target_input)
      result = sentinel_linear_search(sequence, target)
      if result is not None:
          print('{} found at positions: {}'.format(target, result))
      else:
          print('Not found')
subject: add sentinel linear search algorithm