Python using super() for inheritance

Question

Suppose I have 2 files, frontend.py for displaying a GUI and backend.py for database functions. I am having an issue inheriting the database class using super(). from #backend2.py in the managerPage class in #frontend.py

I have the error:

frame = F(container, self) TypeError: init() missing 2 required positional arguments: 'cn' and 'cur'

I believe this has to do with init in the tk.Frame class which i have also inherited in the managerPage class. I believe the selfService class (which I have renamed for my own sake) is credited to user @BryanOakley. Could someone please help me successfully utilise super().

frontend.py.

import backend2

class selfService(tk.Tk, Toplevel):

    def __init__(self, *args, **kwargs):
        #Toplevel.__init__(self)
        self.employeeWindow = None


        tk.Tk.__init__(self, *args, **kwargs)
        self.container = tk.Frame(self)

        self.container.pack(side="top", fill="both", 
        expand = True)

        self.container.grid_rowconfigure(0, 
        weight=1)
        self.container.grid_columnconfigure(0, 
        weight=1)

        self.frames = {}


        selfService.restart = False

        for F in (StartPage, PageOne, PageTwo):

        self.frame = F(self.container, self)

        self.frames[F] = self.frame

        self.frame.grid(row=0, column=0, 
        sticky="nsew")

        self.show_frame(StartPage)


    def show_frame(self, cont):
        self.frame = self.frames[cont]
        self.frame.tkraise()

class managerPage(tk.Frame, 
    validation.account_validation,backend2.Database):
    def __init__(self, parent, controller, cn, cur):
        tk.Frame.__init__(self,parent)
        super().__init__(cn, cur)

        print(self.cn)

backend2.py

class Database():
    def __init__(self):
        self.config = {
        'user': 'root',
        'password': 'root',
        'host': 'localhost',
        'database': 'myDatabase'}

        self.cn = 
        mysql.connector.connect(**self.config)
        self.cur = self.cn.cursor()

You're using inheritance in a way that suggests you shouldn't be using inheritance. Are you certain that you want each page to have its own separate database connection? Ie: if you have 3 pages, you'll have 3 distinct connections to the database. That's an unusual design. — Bryan Oakley
– Bryan Oakley, Commented Jan 29, 2020 at 19:16

Bryan Oakley · Accepted Answer · 2020-01-29 19:18:00Z

0

Inheritance isn't for sharing data between two different objects. Your managerPage should not inherit your Database class. The page can't both be a page and a database at the same time. Each instance would be a separate instance of the database if you used inheritance.

Instead, you should create a single instance of the Database class, and pass that instance to the pages that need it. That, or add a method on the controller which can return the instance.

For example, you can create the database instance in the __init__ of your controller:

class selfService(tk.Tk):

    def __init__(self, *args, **kwargs):
        ...
        self.db = Database()
        ...

Then, in any code that has a reference to the controller you can access the database with self.controller.db, like in the following example:

class managerPage(tk.Frame):
    def __init__(self, parent, controller):
        self.controller = controller
        ...
        print(self.controller.db)

(as a side note, you shouldn't be inheriting from Tk and Toplevel. One or the other, but not both).

edited Jan 29, 2020 at 19:18

answered Jan 29, 2020 at 19:06

Bryan Oakley

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2 Comments

grimReaperZ Over a year ago

Ok. Thanks. But when instantiating the db class in selfService, I am subject to the error: return getattr(self.tk, attr) AttributeError: '_tkinter.tkapp' object has no attribute 'db'

Bryan Oakley Over a year ago

@grimReaperZ: like My first example shows, you have to define self.db.

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