Why doesn't Python have static variables?

Question

There is a questions asking how to simulate static variables in python.

Also, on the web one can find many different solutions to create static variables. (Though I

Answer 1

The idea behind this omission is that static variables are only useful in two situations: when you really should be using a class and when you really should be using a generator.

If you want to attach stateful information to a function, what you need is a class. A trivially simple class, perhaps, but a class nonetheless:

def foo(bar):
    static my_bar # doesn't work

    if not my_bar:
        my_bar = bar

    do_stuff(my_bar)

foo(bar)
foo()

# -- becomes ->

class Foo(object):
    def __init__(self, bar):
        self.bar = bar

    def __call__(self):
        do_stuff(self.bar)

foo = Foo(bar)
foo()
foo()

If you want your function's behavior to change each time it's called, what you need is a generator:

def foo(bar):
    static my_bar # doesn't work

    if not my_bar:
        my_bar = bar

    my_bar = my_bar * 3 % 5

    return my_bar

foo(bar)
foo()

# -- becomes ->

def foogen(bar):
    my_bar = bar

    while True:
        my_bar = my_bar * 3 % 5
        yield my_bar

foo = foogen(bar)
foo.next()
foo.next()

Of course, static variables are useful for quick-and-dirty scripts where you don't want to deal with the hassle of big structures for little tasks. But there, you don't really need anything more than global — it may seem a but kludgy, but that's okay for small, one-off scripts:

def foo():
    global bar
    do_stuff(bar)

foo()
foo()