What is the Python equivalent of static variables inside a function?

Question

What is the idiomatic Python equivalent of this C/C++ code?

void foo() {     static int counter = 0;     counter++;     printf("counter is %d\n", counter); } 

specifically, how does one implement the static member at the function level, as opposed to the class level? And does placing the function into a class change anything?

Answer 1

A bit reversed, but this should work:

def foo():     foo.counter += 1     print "Counter is %d" % foo.counter foo.counter = 0 

If you want the counter initialization code at the top instead of the bottom, you can create a decorator:

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

Then use the code like this:

@static_vars(counter=0) def foo():     foo.counter += 1     print "Counter is %d" % foo.counter 

It'll still require you to use the foo. prefix, unfortunately.

^{(Credit: @ony)}

Answer 2

You can add attributes to a function, and use it as a static variable.

def myfunc():   myfunc.counter += 1   print myfunc.counter  # attribute must be initialized myfunc.counter = 0 

Alternatively, if you don't want to setup the variable outside the function, you can use hasattr() to avoid an AttributeError exception:

def myfunc():   if not hasattr(myfunc, "counter"):      myfunc.counter = 0  # it doesn't exist yet, so initialize it   myfunc.counter += 1 

Anyway static variables are rather rare, and you should find a better place for this variable, most likely inside a class.