Calling a class inside other class

[dan789]

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class Class1:       def __init__(self):         self.atr1 = value1         self.atr2 = value2       def method_1(self):         ???   class Class2:       def __init__(self):         self.atr_new = ???       def method_2(self):         ...

Hi, I want these 2 classes to work together. The Class1 has a lot of methods and is doing an important part of my program. The Class2 is just as an addition to Class1. What I want to use this Class2 for is:
After several code lines in Class1 are realised, it has to call Class2 with some of its atributes. Let´s give an example - Class1 creates a tkinter canvas and doing something there, method_1 should call Class2 with self.atr1 and self.atr2 atributes and that method Class2 should according to these 2 atributes do something in that tkinter canvas.

Can you help me with that? How to connect these 2 classes to work so?

Thank you in advance.

[Larz60+]

to call class2 from class1,

1. Instantiate class 2 in the class1 __init__ method:
   

   1	self.c2 = Class2()

2. when you want to call Class2 method_2 from class1:
   

   1	self.c2.method_2(...)

[stullis]

To do that, you need to instantiate Class2 an attribute in Class1:

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class Class1:        def __init__(self, value1, value2, class2):         self.atr1 = value1         self.atr2 = value2         self.class2 = class2        def method_1(self):         ???    class Class2:        def __init__(self):         self.atr_new = ???        def method_2(self):         ...   x = Class2() y = Class1(1, 2, x)

As needed, you can then access the methods and attributes of class2 by calling self.class2 (e.g. self.class2.method_2() would call method_2() of Class2).

[dan789]

Well, thank you. Until here it works, but I came across one another problem. In Class1 and method_1 I create few variables, let´s call them self.var_1, self.var_2. After their creating I want to call Class2 (method_2) with these two variables. But how to call it with something, what is self to the Class1?

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class Class1:   def method_1(self): self.var_1 = value1 self.var_2 = value2 self.class2.method_2(???)   class Class2:   def method_2(???): ...

What to put instead of "???" ?

[stullis]

You have two options:

1. Pass the two attributes through as arguments to Class2.method_2().
   
2. Add an attribute to Class2 to store Class1. This way, each of them exists inside the other and can access attributes and methods from the other at any time.
   

[Gribouillis]

Use instances, not classes, and keep a pointer to the Class1 instance in Class2

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class Class1:     def __init__(self):         self.c2 = Class2(self)       def method1(self):         self.var1 = 'spam'         self.var2 = 'eggs'         self.c2.method2()       class Class2:     def __init__(self, c1):         self.c1 = c1       def method2(self):         print(self.c1.var1, self.c1.var2)   if __name__ == '__main__':     guido = Class1()     guido.method1()

Output:
spam eggs

[dan789]

@Gribouillis :

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class Class2:     def __init__(self, c1):         self.c1 = c1

What is c1 here? It doesn´t work for me.

@stullis :

When I make it like this:

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class Class1:   def __init__(self): self.c2 = Class2()   class Class2:   def __init__(self): self.c1 = Class1()

it gets into endless calling each other, without any result.

[stullis]

Like Gribouilis said, you need to use class instances, not the class itself. In his example:

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class Class1:     def __init__(self):         pass       def add_class2(self, c2):         self.c2 = c2   class Class2:     def __init__(self, c1):         self.c1 = c1   # Instantiate them c1 = Class1() c2 = Class2(c1) c1.add_class2(c2)

[Gribouillis]

What is c1 here? It doesn´t work for me.

c1 is a Class1 instance that needs to be passed to Class2's constructor. If you run my code above, it necessarily works for you. At line 3 in the call self.c2 = Class2(self), the Class1 instance 'self' is passed as the c1 argument in Class2.__init__()

[dan789]

Thank you, works now and I finally understand how. :)