What is a static variable in Python?

In Python, a static variable is a variable belonging to the class rather than a specific instance of the class. Its value is shared among all instances of the class.

Main characteristics:

• Scope: Within the class.
• Lifetime: Exists throughout the runtime of the program.
• Access: Can be accessed via the class name or through an instance of the class (though accessing via the class name is preferred to indicate its static nature).

Example of usage:

class MyClass:
    # Static variable
    static_variable = 10

    def __init__(self, instance_variable):
        # Instance variable
        self.instance_variable = instance_variable

# Accessing static variable via class name
print(MyClass.static_variable)

# Creating instances
obj1 = MyClass(20)
obj2 = MyClass(30)

# Accessing static variable via instances
print(obj1.static_variable)
print(obj2.static_variable)

# Changing static variable via class name
MyClass.static_variable = 15

# The value has changed for all instances
print(obj1.static_variable)
print(obj2.static_variable)

In this example, static_variable is a static variable. It exists as a single instance for the entire MyClass class, and its value is shared among objects obj1 and obj2. Changing the value via the class name MyClass.static_variable = 15 affects all instances.

It is important to distinguish static class variables from instance variables (self.instance_variable), which are unique to each object (instance) of the class.