I want to count the number of times a given function has been called.
So, I made a countcalls decorator to give my functions a __callcount attribute which gets incremented on each call. Simple enough.
My issue is getting the __callcount value back out later.
Here's my code:
import functools
def countcalls(f):
f.__callcount = 0
@functools.wraps(f)
def _countcalls(*args, **kwds):
f.__callcount += 1
print(' Called {0} time(s).'.format(f.__callcount))
return f(*args, **kwds)
return _countcalls
@countcalls
def fib(n):
if n < 0:
raise ValueError('n must be > 0')
if n == 0 or n == 1:
return 1
return fib(n-1) + fib(n-2)
if __name__ == '__main__':
print('Calling fib(3)...')
x = fib(3)
print('fib(3) = {0}'.format(x))
print('Calling fib(3) again...')
x = fib(3)
print('fib(3) = {0}'.format(x))
print('fib was called a total of {0} time(s).'.format(fib.__callcount))
Which generates the following output (Python v3.3.0):
Calling fib(3)...
Called 1 time(s).
Called 2 time(s).
Called 3 time(s).
Called 4 time(s).
Called 5 time(s).
fib(3) = 3
Calling fib(3) again...
Called 6 time(s).
Called 7 time(s).
Called 8 time(s).
Called 9 time(s).
Called 10 time(s).
fib(3) = 3
fib was called a total of 0 time(s).
Why does fib.__callcount equal 0 on the last line? As the output shows, __callcount gets incremented, and persists between calls of fib.
What am I missing?
f.__callcount = [0]
..........
f.__callcount[0] = f.__callcount[0] + 1
......
print('fib was called a total of {0} time(s).'.format(fib.__callcount[0]))
It works.
Maybe ther's something more pythonic
This does what you want. I got it here- https://wiki.python.org/moin/PythonDecoratorLibrary#Alternate_Counting_function_calls
class countcalls(object):
"Decorator that keeps track of the number of times a function is called."
__instances = {}
def __init__(self, f):
self.__f = f
self.__numcalls = 0
countcalls.__instances[f] = self
self.__doc__ = f.func_doc
self.__name__ = f.func.func_name
def __call__(self, *args, **kwargs):
self.__numcalls += 1
return self.__f(*args, **kwargs)
def count(self):
"Return the number of times the function f was called."
return countcalls.__instances[self.__f].__numcalls
@staticmethod
def counts():
"Return a dict of {function: # of calls} for all registered functions."
return dict([(f.__name__, countcalls.__instances[f].__numcalls) for f in countcalls.__instances])
@countcalls
def fib(n):
if n < 0:
raise ValueError('n must be > 0')
if n == 0 or n == 1:
return 1
return fib(n-1) + fib(n-2)
if __name__ == '__main__':
print('Calling fib(3)...')
x = fib(3)
print('fib(3) = {0}'.format(x))
print('fib was called a total of {0} time(s).'.format(fib.count()))
print('Calling fib(3) again...')
x = fib(3)
print('fib(3) = {0}'.format(x))
print('fib was called a total of {0} time(s).'.format(fib.count()))
The function object you are adding an attribute to is a different object than the 'original' function. Try this:
import functools
def countcalls(f):
f.__callcount = 0
@functools.wraps(f)
def _countcalls(*args, **kwds):
f.__callcount += 1
print 'id(f):', id(f)
print(' Called {0} time(s).'.format(f.__callcount))
return f(*args, **kwds)
return _countcalls
@countcalls
def fib(n):
"""fibinacci"""
if n < 0:
raise ValueError('n must be > 0')
if n == 0 or n == 1:
return 1
return fib(n-1) + fib(n-2)
if __name__ == '__main__':
print('Calling fib(3)...')
x = fib(3)
print 'id(fib):', id(fib)
"""
>>>
Calling fib(3)...
id(f): 45611952
Called 1 time(s).
id(f): 45611952
Called 2 time(s).
id(f): 45611952
Called 3 time(s).
id(f): 45611952
Called 4 time(s).
id(f): 45611952
Called 5 time(s).
id(fib): 45612016
>>>
"""
Well, here's the reason, after a bit of help. Thanks guys!
The issue is that functions are immutable. e.g.
>>> def f(func):
... return func()
...
>>> def g():
... return 'sunflower seeds'
...
>>> id(g)
139636515497336
>>> g = f(g)
>>> id(g)
139636515515112
So, the only way to get the function f we assigned the __callcount attribute to in the definition of countcalls is to return that function from callcount. But we're already returning the inner function _countcalls. We can return both f and _countcalls but that messes up the @countcalls decorator syntax.
You can still do it this way, it's just not as pretty.
import functools
def countcalls(f):
f.__callcount = 0
@functools.wraps(f)
def _countcalls(*args, **kwds):
f.__callcount += 1
print(' Called {0} time(s).'.format(f.__callcount))
return f(*args, **kwds)
return f, _countcalls
def fib(n):
if n < 0:
raise ValueError('n must be > 0')
if n == 0 or n == 1:
return 1
return fib(n-1) + fib(n-2)
if __name__ == '__main__':
counter, fib = countcalls(fib)
print('Calling fib(3)...')
x = fib(3)
print('fib(3) = {0}'.format(x))
print('Calling fib(3) again...')
x = fib(3)
print('fib(3) = {0}'.format(x))
print('fib was called a total of {0} time(s).'.format(counter.__callcount))
Long story short, just use the class from the Python Decorator Library. :D
