def c(f):
def inner(*args, **kargs):
inner.co += 1
return f(*args, **kargs)
inner.co = 0
return inner
@c
def fnc():
pass
if __name__ == '__main__':
fnc()
fnc()
fnc()
print(fnc.co)
please explain the final output: 3
I am aware of the functionality of decorators but I'm still not getting the output.
First, let's unpack what the decorator syntax does. When you write this:
@c
def fnc():
pass
… it's equivalent to this:
def fnc():
pass
fnc = c(fnc)
Now look at what c does: It creates a new function, named inner, and sets inner.co to 0, and returns inner to be used in place of fnc. So, now your code is equivalent to this:
def fnc():
pass
def inner(*args, **kargs):
inner.co += 1
return fnc(*args, **kargs)
inner.co = 0
fnc = inner
So, when you call fnc() three times, you're calling inner each time. So it increments inner.co three times. And since inner and fnc are the same thing, inner.co and fnc.co are the same thing. So print(fnc.co) prints 3.
In python, functions are "first class objects" (See What are "first class" objects?). This means you can set attributes on them. You define your function fnc here, and the decorator c adds a property to that function object fnc.co. Its a little weird that the inner.co = 0 initialization is done after the wrapping function is declared, but since inner won't get called until after the co property is defined it doesn't matter. Then in inner the co property gets incremented each time the function is called.
