python: How to assign a class function result to a class variable in the same class

Question

I am a beginner to python and want to understand the python class modules and class variables.

I just want to assign a class function's return value to the class variable. I tried in different ways, are these valid in python?

Sample code:

class Example():
    def class_member(self):
        dict_1 = {'k1' : 'v1','k2' : 'v2'}
        return dict_1

    class_var = class_member()
    print(class_var)

x_obj =  Example()

Errors:

    class_var = class_member()
TypeError: class_member() takes exactly 1 argument (0 given)

    class_var = class_member(self)
NameError: name 'self' is not defined

    class_var = Example.class_member()
NameError: name 'Example' is not defined

Answer 1

There are a number of issues with your class usage here. Error 1 occurs because in your class definition you've stated that class_member() takes in 'self', which is a reference to the current instance of the class, which you have not created. Error 2 occurred because 'self' has been passed into class_member() as if it was a variable. Error 3 is most likely caused by the class definition not being in the file that requires it.

    class Example(): 
        def __init__ (self):
            self.dict_1 = {'k1' : 'v1','k2' : 'v2'} 

        def class_member (self): 
            return self.dict_1

    my_object = Example()
    class_var = my_object.class_member()
    print(class_var)

Be sure to check out the Python docs first next time. https://docs.python.org/3/tutorial/classes.html

Answer 2

If you need to store variable inside a class, You might need an initialization function __init__ with double underscores on opposite sides. And you will need a self in front of the 'class_var'. Which will mean that the variable has become part of the class. And also you will need a self in front of the 'class_member' function. Which will mean that the function belongs to this class.

class Example:
    def __init__(self):
        self.class_member()

    def class_member(self):
        dict_1 = {'k1' : 'v1','k2' : 'v2'}
        self.class_var = dict_1

e = Example()

print(e.class_var) #prints {'k1': 'v1', 'k2': 'v2'}

Answer 3

Another way to achieve this is to make dict_1 property of the Example class and then return it in the class_member function.

class Example():
  dict_1 = {'k1' : 'v1','k2' : 'v2'}
  def class_member(self):
    return self.dict_1

example = Example()

print(example.dict_1) # prints {'k1': 'v1', 'k2': 'v2'}
print(example.class_member()) # prints {'k1': 'v1', 'k2': 'v2'}

I would recommend to go through this link and read it in detail.