Question

Possible Duplicate:
Static class variables in Python
What is the Python equivalent of static variables inside a function?

How can I use static fields in Python ?

for example i want to count how many times the function has been called – how can i do this ?

Answer 1

If you wish to count how many times a method has been called, no matter which instance called it, you could use a class member like this:

class Foo(object):
    calls=0            # <--- call is a class member
    def baz(self):
        Foo.calls+=1

foo=Foo()
bar=Foo()
for i in range(100): 
    foo.baz()
    bar.baz()
print('Foo.baz was called {n} times'.format(n=foo.calls))
# Foo.baz was called 200 times

---

When you define calls this way:

class Foo(object):
    calls=0            

Python places the key-value pair (‘calls’, 0) in Foo.__dict__.

It can be accessed with Foo.calls.
Instances of Foo, such as foo=Foo(), can access it with foo.calls as well.

To assign new values to Foo.calls you must use Foo.calls = ....
Instances can not use foo.calls = ... because that causes Python to place a new and different key-value pair in foo.__dict__, where instance members are kept.