code: def get_key_for_value(dict_obj, value, default=None):
      
      for k, v in viewitems(dict_obj):
          if v == value:
              return k
      return default
docs: >>> get_key_for_value({0: 'what', 'k': 'ever', 'you': 'want', 'to find': None}, 'you')
      >>> get_key_for_value({0: 'what', 'k': 'ever', 'you': 'want', 'to find': None}, 'you', default='Not Found')
      'Not Found'
      >>> get_key_for_value({0: 'what', 'k': 'ever', 'you': 'want', 'to find': None}, 'other', default='Not Found')
      'Not Found'
      >>> get_key_for_value({0: 'what', 'k': 'ever', 'you': 'want', 'to find': None}, 'want')
      'you'
      >>> get_key_for_value({0: 'what', '': 'ever', 'you': 'want', 'to find': None, 'you': 'too'}, 'what')
      0
      >>> get_key_for_value({0: 'what', '': 'ever', 'you': 'want', 'to find': None, 'you': 'too', ' ': 'want'}, 'want')
      ' '