Static member of a function in Python ?
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 ?
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 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 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
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