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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 ?
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.
Here's a decorator adding counting to a function.
import functools def count_calls(func): @functools.wraps(func) def decor(*args, **kwargs): decor.count += 1 return func(*args, **kwargs) decor.count = 0 return decor Usage:
>>> @count_calls ... def foo(): ... pass ... >>> foo.count 0 >>> foo() >>> foo.count 1 
count_calls
Here is some example counting the number of calls of all objects of the same class:
class Swallow(): i = 0 # will be used for counting calls of fly() def fly(self): Swallow.i += 1 And this is the proof:
>>> a = Swallow() >>> b = Swallow() >>> a.fly() >>> a.i 1 >>> Swallow.i 1 >>> b.fly() >>> b.i 2 >>> Swallow.i 2 so you can read it by giving the object name or class name.
Here's one simplistic way to do it:
def func(): if not hasattr(func, 'counter'): func.counter = 0 func.counter += 1 counter = 0 # Not the same as `func.counter` print(func.counter) Or if you don't like the if being executed on every call, you can do:
def func(): func.counter += 1 print(func.counter) func.counter = 0 