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

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

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

Itll still require you to use the foo. prefix, unfortunately.

^{(Credit: @ony)}

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 dont 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 doesnt 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.

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

One could also consider:

def foo():
    try:
        foo.counter += 1
    except AttributeError:
        foo.counter = 1

Reasoning:

• much pythonic (ask for forgiveness not permission)
• use exception (thrown only once) instead of if branch (think StopIteration exception)