🔄 How to define a class variable shared among all instances of a class in Python?

In Python, if you want to define a variable that is shared across all instances of a class, you should define it outside of any method but inside the class — this is called a class variable.

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✅ Correct answer to the question:

> How would you define a class variable that is shared among all instances of a class in Python?

🟢 Option 2: Outside of any method at the class level

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🔍 Let’s review the other options:

🔴 Option 1: Inside the constructor method using self
This creates an instance variable, specific to each object, not shared.

🔴 Option 3: As a local variable inside a method
Local variables are temporary and only exist inside the method scope.

🔴 Option 4: As a global variable outside the class
Global variables are shared across the entire program, not specific to class instances.

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🚗 Simple Example: Class Variable in Action

class Car:
    wheels = 4  # ✅ class variable, shared across all instances

    def __init__(self, brand, color):
        self.brand = brand  # instance variable
        self.color = color  # instance variable

car1 = Car("Toyota", "Red")
car2 = Car("BMW", "Blue")

print(Car.wheels)   # Output: 4
print(car1.wheels)  # Output: 4
print(car2.wheels)  # Output: 4

Car.wheels = 6  # changing the class variable

print(car1.wheels)  # Output: 6
print(car2.wheels)  # Output: 6

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💡 Key Takeaways:
- self. creates instance variables → unique to each object.
- Class-level variables (outside methods) are shared across all instances.
- Perfect for shared attributes like constants, counters, or shared settings.



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👨‍💻 From: https://t.iss.one/DataScienceQ

⁉️ Interview question
In Python, what happens when a class inherits from multiple classes that have a method with the same name, and how does the Method Resolution Order (MRO) determine which method gets called?

Simpson:
When a class inherits from multiple parent classes with a method of the same name, Python uses the **Method Resolution Order (MRO)** to decide which method is invoked. The MRO follows the **C3 linearization algorithm**, which ensures a consistent and deterministic order based on the inheritance hierarchy. This means that if you call the method, Python traverses the classes in a specific sequence defined by the MRO, starting from the child class and moving through parents in a depth-first, left-to-right order. If a method is found in one of the parent classes before others, it will be used, even if other parents also define the same method. The MRO can be inspected using `ClassName.mro()` or `help(ClassName)`. However, if there’s an ambiguity in the inheritance structure—such as a diamond pattern without proper resolution—the C3 algorithm still resolves it, but unexpected behavior may occur if not carefully designed. This makes understanding MRO crucial for complex inheritance scenarios.

#️⃣ tags: #Python #AdvancedPython #Inheritance #MethodResolutionOrder #MRO #OOP #ObjectOrientedProgramming #InterviewQuestion

By: t.iss.one/DataScienceQ 🚀