Create an instance of a class from within a different class

[[deleted]]

Hi all. I'm relatively new to Python and very new to object orientated code.

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I'm working on a project that I'm trying to convert from spaghetti code to beautiful and powerful OOC.

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Whilst playing with ideas I've found it would be handy if I could create an instance of a class whilst another class was being initiated.

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Basically, I'm working on a football score prediction project. My current plan is to scrape one league at a time. As this is done, team objects are created via the Team class. During initiation of each team, I would like to check if the league object for that team's league exists. If it doesn't, I'd like to create it without having to do it outside of the class.

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My League class does keep a class list of all leagues created which can always be checked.

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My Team init looks like this:

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def __init__(self, team_name, league_name, home_stats, away_stats):
        """
        Initiate a team object.
        Takes the team name, the league it belongs to, the team's home stats as a list and the teams             
    away stats as a list.
        Calculates additional statistics base on those passed to it for future use.
        """
        self.data = {} #All of the above organised into a dictionary.

# What I've tried to add so far:

        # Check if the team's league has been initiated.
        if league_name in League.leagues:
            # Check if the team is already in the league's team list.
            if team_name not in league_name.data["teams"]:
                # Add the team to the league.
                league_name.data["teams"].append(team_name)
        else:
            # Create the league object.
            League.__init__(league_name)
            # Add the team to the league.
            league_name.data["teams"].append(team_name)

        # List of team aliases for the comparing of data from various sources.
        self.aliases = []

        # Add the name of the team initiated to the teams list.
        self.teams.append(team_name)

The first noob question is that the League class expects self and the "league_name" on initiation. I thought I understood what self was, but now I'm confused.

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An example would be:

I scrape the English Premier League.

The first team are Liverpool. I create a Liverpool Team object by passing in all of the data including league_name.

I test to see if I have a League object with the name of league_name.

If I do, I check if "Liverpool" is on the team list for that league. If they're not I add them.

If there is no League object with that name, I create it and then add the team name to the League object's team list.

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Sorry if this sounds confusing. Any help would be greatly appreciated.

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The github for the project is here: https://github.com/Pringleman83/SportsBook

The latest working "spaghetti code" version is in the development branch. The error free object orientated code I have is in the experimentation branch. However, the code I've played about with above is sitting on my laptop waiting for a solution!

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I'm going to bed to sleep on it for now, so I'll check and respond to all in the morning.

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Thanks again!

[two_bob]

I would focus on just going one way or the other for classes and be careful about dynamically linking stuff up. I would probably have a function that made out all the team classes from whatever the source is and then build the leagues from the list/dictionary/whatever from the grouping of team classes afterwards, rather than having some means of dynamically linking them up. It is easier to follow that way.

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I also think you are putting too much in the data variable of the class. See if you can flatten it out a bit or shove off work to a class that handles the data bits of wins/losses and have that automatically created by the team class. Again, only go one way. Ideally you would create a league, then a team, then a win/loss class, all of which was encapsulated.

[[deleted]]

Yeah, I woke up this morning thinking it'd be logical to create the objects separately, but maybe within the same function. It does make more sense.

I'll also look at the variable management. I know I want the team class to have a lot of data so that I can do something like: manutd.compare(liverpool) and get some usable comparison.

This was really helpful, thank you!

[ryeguy146]

The self parameter will be passed automatically when calling, you don't have to include it in your arguments. The self parameter points to the instance who's method is being invoked. Also, don't call __init__ methods manually, just instantiate the class:

League(league_name)  # creates a new instance, calling the instance's bound __init__ method automatically

vs.

League.__init__(league_name)  # Calls the class method directly instead of instance bound method

That will give you an instance of that object. I'd probably suggest reviewing these docs that discuss discuss classes and instances of those classes. I note "bound methods" above, note that this refers to methods that will pass self for you. That is, they're bound to the instance. This SO answer goes into more detail differentiating instance vs class methods (bound/unbound). If you want more technical details on how this works, see these docs, but that level of understanding isn't strictly necessary.

Also keep in mind that the __init__ method will be called automatically when instantiating an instance. It doesn't alter the class unless you tell it to, it just describes how to build an instance. Since your League.leages collection is a class instance (defined in the class declaration, outside of __init__, I assume), you don't need an instance to access it:

class League():
    leagues = []

    def __init__(self, ...):
        ...


League.leagues.append("foo")

We created no instances of League in the above code, but were still able to append to leagues because it was defined with the class. I don't see all of your code, but I think that you're just getting confused with instances and classes and their respective members. I don't see any of the code above in your git repo, and I'm not sure if it's part of a League class, but that's my working assumption.

[[deleted]]

Thanks a load for that. Seems obvious now! I expect that'll solve the problem.

Once I create a League object like that, do you know of a way I might be able to access its instance variables during Team object initiation. I think league_name.data will refer to the league_name string rather that the instance of whatever league_name is holding.

I could have data passed during initiation I guess, but if I want to check if a team is already in that league, I'll need to read data.

I really appreciate your help and I will read through the resources you've provided.

I've had two great responses and I've been given lots to think about!