Static member of a function in Python ?

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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 ?

Asked By: Patryk

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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.

Answered By: unutbu

Answer 2

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.

Answered By: Tadeck

Answer 3

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

Answered By: yak

Answer 4

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

Answered By: Paul Manta

Static member of a function in Python ?

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