59   1. 

    59   1. Consider the following use case: We are given a large list of

    60      items called *data* where each item is a again a list with three

    61      values: username, which is a string; status of the user which

    62      can be one of the following three strings 'new', 'valid' or

    63      'invalid'; and the last login time which is a datetime Python

    64      object.  Write a function called **query** that takes a filter

    65      dictionary as a parameter and returns the result of the items in

    66      the *data* list. They keys of the dictionary can be 'user',

    67      'status' and 'logtime' and their corresponding values can be any

    68      of the valid values for the corresponding key. Example filter

    69      dictionary::

    70 

    71        filter = {

    72            'user': 'john'

    73            'status': 'new'

    74            }

    75 

    76      Place your function in a file called query.py. Before writing the

    77      actual function, follow the test driven development

    78      approach. First write a stub, fail the tests and then write the

    79      code and make sure the tests pass. Specifically use unittest

    80      framework to test this function. Place your tests in a file

    81      called test_query.py

    82 

    83      A developer wrote a small utility function in a file named

    84      user_utils.py which uses your **query** function which looks as

    85      follows::

    86 

    87        def login_util(user=None):

    88            """Takes a user name and returns his last login time if the

    89            user is a valid user, else return None. If the user is

    90            'host' it returns the last login time of all the users.

    91            """

    92 

    93            filter_dict = {

    94                'user': user

    95                'status': 'active'

    96                }

    97 

    98            if user == 'host':

    99                filter_dict['status'] + ['new', 'invalid']

   100 

   101            return query(filter_dict)

   102 

   103      Unfortunately the developer did not provide us with the test

   104      cases. We wrote the following test cases for you to only discover

   105      that the function miserably fails. 

   106 

   107      The tests were placed in a file called test_user_utils.py and we

   108      have used the unittest framework::

   109 

   110        import query

   111        import user_utils

   112        import unittest

   113 

   114        class TestUserUtils(unittest.TestCase):

   115         

   116            def setUp(self):

   117                """Boiler plate method to provide common data to all

   118                the test methods.

   119                """

   120                self.test_names = ['Alex', 'Guido', 'Thomas', 'host',

   121                    'Tom', 'James']

   122                self.data_len = len(query.data)

   123 

   124            def test_login_utils(self):

   125                """Tests for the login_utils function.

   126                """

   127 

   128                for name in self.test_names:

   129                    if name == 'host':

   130                        assertEqual(len(user_utils.login_utils(name)), self.data_len)

   131                    else:

   132                        assertLess(len(user_utils.login_utils(name)), self.data_len)

   133 

   134            def tearDown(self):

   135                """Boiler plate method to clean up all the data created

   136                for tests.

   137                """

   138 

   139                del self.test_names

   140                del self.data_len

   141 

   142      Fix the bug, run the tests to make sure the function passes the

   143      tests and if possible refactor the code with a better approach.