How Can I Simulate Static Function Variables in Python?

Python Equivalent of Static Function Variables

Problem:
How does Python implement static variables within functions, similar to C/C 's static member variables defined at the function level?

Answer:

In Python, there is no direct equivalent for static variables within functions. However, a similar functionality can be achieved using a combination of nested functions and closures:

def foo():
    def counter():
        if not hasattr(foo, "counter_value"):
            foo.counter_value = 0
        foo.counter_value += 1
        return foo.counter_value
    return counter

Here, the function foo() defines a nested function counter(). The outer function foo() serves as a closure for counter(), providing it with an isolated namespace.

To access and increment the counter, you would call:

counter = foo()
counter()  # Initializes the counter
counter()  # Increments the counter

Decorator Approach:

Another approach is to use a decorator to create a static variable:

def static_vars(**kwargs):
    def decorate(func):
        for k in kwargs:
            setattr(func, k, kwargs[k])
        return func
    return decorate

@static_vars(counter=0)
def foo():
    foo.counter += 1
    return foo.counter

This syntax allows you to initialize and access the static variable more conveniently, but it requires using the foo. prefix.

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