by: Jayson McleodPosted on

Python emerges as a multifaceted programming language, presenting an expansive toolkit that enables developers to craft sophisticated and streamlined code. Within its myriad capabilities, especially in the domain of object-oriented design, the incorporation of class-bound static variables holds a special place. This piece offers an in-depth exploration of static variables, spotlighting their role and furnishing a guide on their adept use.

What is a Static Variable?

A static variable, within the domain of object-oriented programming, serves a distinct role compared to typical instance variables. Unlike instance variables, which have distinct values for each object instance, a static variable is associated with the class itself rather than any specific instance. This unique association means that regardless of how many objects of a class are instantiated, there is only a single copy of the static variable. All object instances of that class access and share this single variable. As a result, any changes made to the static variable by one instance become immediately visible to all other instances, underlining its shared nature across the entire class landscape.

Key Characteristics of Static Variables

Shared among InstancesAll instances of a class share the same static variable. Any modification to this variable by one instance will be visible to other instances.
Memory EfficientSince only one copy of the static variable is created, it helps in conserving memory, especially when multiple instances of a class are created.
No Dependency on Object CreationA static variable exists even if no objects of the class have been instantiated. They are tied to the class, not the object.

When to Use Static Variables?

  • Shared Configuration: If all instances of a class need to work with a common configuration or data, static variables can be used;
  • Counter or Tracker: To keep track of the number of objects created for a class or other similar global metrics, static variables can come in handy;
  • Constants: When you have values related to a class that shouldn’t change irrespective of the number of instances or actions on those instances, static variables serve as a great choice.

Python’s Class-Level (Static) Variables 

computer monitor with code, a keyboard, mouse, a cup of coffee, and a potted plant on the table

 

In object-oriented programming, when a variable is established within the boundaries of a class yet remains outside its functions, it is often termed as a class-level or static variable. This specific type of variable is uniquely accessible through the class’s name rather than through its individual instances. It’s crucial to note that this static variable operates independently and doesn’t clash with other member variables, even if they share the same name.

class Fruit(object):
    count = 0
    def __init__(self, name, count):
        self.name = name
        self.count = count
        Fruit.count = Fruit.count + count

def main():
    apples = Fruit("apples", 3);
    pears = Fruit("pears", 4);
    print apples.count
    print pears.count
    print Fruit.count
    print apples.__class__.count # This is Fruit.count
    print type(pears).count      # So is this

if __name__ == '__main__':
    main()

Conclusion

Static variables in Python provide a useful way to store data that should be shared among all instances of a class. While they bring in memory efficiency and a clear separation of shared data, it’s essential to use them judiciously and be aware of their shared nature. With a good understanding and the right usage, static variables can be a powerful tool in a developer’s arsenal.

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