Using Inheritance in Python

The first thing we need to do is create our class and have it inherit from the Employee class. This will move our script forward. Let's create the manager.py file and create the Manager class.

~/manager.py

from employee import Employee

class Manager(Employee):
    pass

Now if we run the using_inheritance.py script, we should see the following error:

$ python3.7 using_inheritance.py
Traceback (most recent call last):
  File "using_inheritance.py", line 23, in <module>
    manager_1.meetings == []
AttributeError: 'Manager' object has no attribute 'meetings'

The error we're running into shows we don't have a meetings attribute, and since we want to default this to an empty list, we'll need to customize the __init__ method for our class. The method signature needs to be exactly like Employee, so we'll copy that over, but then we'll need to utilize super before finally adding our new attribute.

~/manager.py

from employee import Employee

class Manager(Employee):
    def __init__(self, name, email_address, title, phone_number=None):
        super().__init__(name, email_address, title, phone_number)
        self.meetings = []

This should be enough to move us to the next error:

$ python3.7 using_inheritance.py
Traceback (most recent call last):
  File "using_inheritance.py", line 32, in <module>
    manager_1.schedule_meeting(invitees, meeting_time1)
AttributeError: 'Manager' object has no attribute 'schedule_meeting'

The schedule_meeting method needs to take an invitees list and a time that will be a datetime object. We will use this information to build a simple dictionary, add it to meetings, and then sort meetings by the time attribute. Let's implement this method now:

~/manager.py

from employee import Employee

class Manager(Employee):
    def __init__(self, name, email_address, title, phone_number=None):
        super().__init__(name, email_address, title, phone_number)
        self.meetings = []

    def schedule_meeting(self, invitees, time):
        self.meetings.append({"invitees": invitees, "time": time})
        self.meetings.sort(key=lambda m: m["time"])

Here's the next error we will see with this method implemented:

$ python3.7 using_inheritance.py
Traceback (most recent call last):
  File "using_inheritance.py", line 42, in <module>
    result = manager_1.run_next_meeting()
AttributeError: 'Manager' object has no attribute 'run_next_meeting'

The last method we need to implement is the run_next_meeting method that will remove and return the first meeting dictionary in the meetings list. Thankfully, this can easily be done by using the list.pop method with the argument of 0:

~/manager.py

from employee import Employee

class Manager(Employee):
    def __init__(self, name, email_address, title, phone_number=None):
        super().__init__(name, email_address, title, phone_number)
        self.meetings = []

    def schedule_meeting(self, invitees, time):
        self.meetings.append({"invitees": invitees, "time": time})
        self.meetings.sort(key=lambda m: m["time"])

    def run_next_meeting(self):
        return self.meetings.pop(0)

With this implementation, we should have fully implemented everything required for the using_inheritance.py script to successfully execute.

$ python3.7 using_inheritance.py