How do I count the number of calls of a function in Python 3.6?

Question

I want to count the number of calls of the function f inside of inc . How should I modify the function main to do it?

I have this code:

def inc(f):
    f()
    f()

def main():
    a = 0
    def f():
        a += 1
    inc(f)
    print(a)  # should print 2

main()

But it leads to the error:

Traceback (most recent call last):
  File "main.py", line 11, in <module>
    main()
  File "main.py", line 9, in main
    inc(f)
  File "main.py", line 2, in inc
    f()
  File "main.py", line 8, in f
    a += 1
UnboundLocalError: local variable 'a' referenced before assignment

Answer 1

The usual way is to create an attribute func.invocations for your function func , like

def func(a):
    func.invocations += 1
    return a + 1

func.invocations = 0

and use it like

func(1)    # 2
func(10)   # 11
func.invocations  # 2

To make the whole thing more reusable and readable you can also create a decorator counter that allows you to count the number of calls on any function you like:

import functools

def counter(fn):
    @functools.wraps(fn)
    def helper(*args, **kargs):
        helper.invocations += 1
        return fn(*args, **kargs)
    helper.invocations = 0
    return helper

and then use it like

@counter
def func(a):
    return a + 1

func(1)    # 2
func(10)   # 11
func.invocations # 2

Answer 2

def inc(f):
    f()
    f()

def main():
    a = 0
    def f():
        nonlocal a
        a += 1
    inc(f)
    print(a)  # should print 2

main()

Make a nonlocal in f()

Answer 3

If you are looking for a simple solution, a global variable would do the trick.

reps = 0

def f():
    global reps 
    reps  += 1
    # do your func stuff here

f()
f()
f()
f()  # called f() 4 times
print(reps)  # -> 4

Answer 4

You try this:

def inc(f):    
    f()    
    f() 


def main():    
    a = 0     
    def f():     
        f.counter += 1    
    f.counter =0    
    inc(f)     
    print(f.counter) 


main()

How functions are objects in python you can create an attribute to count the number of call to that function