In Python 2.7, how can I return calculations without defining variables in the constructor?

Question

My question is about getter/setter-type functionality in Python. I have a class, Week_Of_Meetings, that takes a blob of data from my Google Calendar and does some calculations on it.

wom = Week_Of_Meetings(google_meetings_blob)

I want to be able to return something like:

wom.total_seconds_in_meetings() # returns 36000

But, I'm not understanding how the getters/setters-type @property decorator can help me do this. In Java, I would use member variables, but you don't interact with them the same way in Python. How can I return calculations without starting with them in the constructor?

Class Week_Of_Meetings:

    def __init__(self, google_meetings_blob) 
        self.google_meetings_blob = google_meetings_blob

    def get_meetings_list(self, google_meetings_blob):
        meetings_list = []
        for meeting_id, meeting in enumerate(self.google_meetings_blob, 1):
            summary = self._get_summary(meeting)
            start = parse(meeting['start'].get('dateTime', meeting['start'].get('date')))
            end = parse(meeting['end'].get('dateTime', meeting['end'].get('date')))
            duration = end - start
            num_attendees = self._get_num_attendees(meeting.get('attendees'))

            m = Meeting(meeting_id, summary, start, end, duration, num_attendees)
            meetings_list.append(m)
        return meetings_list


    def _get_summary(self, meeting):
        summary = meeting.get('summary', 'No summary given')
        return summary


    def _get_num_attendees(self, num_attendees):
        if num_attendees == None:
            num_attendees = 1 # if invited only self to meeting
        else:
            num_attendees = len(num_attendees)
        return num_attendees

When I add self.total_seconds_in_meetings to the

__init__() 

I get "NameError: global name 'total_seconds_in_meetings' is not defined." That makes sense. It hasn't been defined. But I can't define it when it's supposed to be the result of calculations done on the google_meetings_blob. So, I'm confused where the 'total_seconds_in_meetings' goes in the class.

Thank you for the help!

Answer 1

Of course Python has member variables. How would classes work without them? You can set and get any instance data via self, as you are already doing with self.google_meetings_blob in __init__.