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61. Instance vs Class Variables

1. Introduction​

Python classes can define two types of variables:

  • Instance variables → unique to each object.
  • Class variables → shared across all objects.

2. Instance Variables​

Defined inside __init__ and tied to self.

class Dog:
    def __init__(self, name):
        self.name = name  # instance variable

d1 = Dog("Buddy")
d2 = Dog("Max")
print(d1.name, d2.name)

Output:

Buddy Max

3. Class Variables​

Defined outside methods, shared by all objects.

class Dog:
    species = "Canine"  # class variable
    def __init__(self, name):
        self.name = name

d1 = Dog("Buddy")
d2 = Dog("Max")
print(d1.species, d2.species)

Output:

Canine Canine

4. Modifying Instance vs Class Variables​

d1.species = "Wolf"  # creates new instance variable
print(d1.species, d2.species)  # Wolf Canine

Dog.species = "Wolf"  # modifies class variable
print(d1.species, d2.species)  # Wolf Wolf

5. Best Practices​

  • Use instance variables for object-specific data.
  • Use class variables for constants or shared defaults.

6. Next Steps​

✅ You now understand instance vs class variables.
Next: Methods and behaviors.