Python Classes: behavior of calling class methods inside constructor

Question

class User:

    def __init__(self, name, age):
        self.name = name
        self.age = age
        self.say_hello()

    def say_hello(self):
        print(f"Hi my name is {self.name} and I am {self.age}")

user = User("Cristian", 19)

output:

**Hi my name is Cristian and I am 19**

Hello! I have a question about this code. We know that when we create an instance of a class, the constructor is executed, right?; in the code we can see a say_hello method that is called inside the constructor, how is this possible if the say_hello method is created after the constructor, how can we call something that is not previously defined? 🤔

When you create an instance of the class, the whole class has been defined. Also Python doesn't resolve references like say_hello() until it's actually executing the code. — vaizki
– vaizki, Commented Sep 27, 2022 at 6:28
Right. That's a key point. The code in the constructor is not executed until you create an object -- in the last line of your example. By that time, the class has been completely read and parsed. As long as say_hello has been defined by that point, it's all good. — Tim Roberts
– Tim Roberts, Commented Sep 27, 2022 at 6:34
"Defining a method inside the constructor" would look like self.say_hello = lambda: ... inside __init__. Which is not what you're doing. — deceze
– deceze ♦, Commented Sep 27, 2022 at 6:51

Abirbhav G. · Accepted Answer · 2022-09-27 08:34:08Z

1

As per your code, the say_hello() method is defined before it is called. The say_hello() is called from __init__() that's true, but __init__() is called when you are creating your object user = User("Cristian", 19)

So the statement responsible for calling say_hello() is creation of object and definition of say_hello() appears before it is called.

Hope this suffice your query.

edited Sep 27, 2022 at 8:34

Abirbhav G.

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answered Sep 27, 2022 at 6:57

Rupal Shah

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