decorator

def counter(fn):

count = 0

def inner(*args, **kwargs):

nonlocal count

count += 1

print('Function {0} was called {1} times'.format(fn.__name__, count)) # {0} = function name (fn.__name__); (1) = count

return fn(*args, **kwargs)

return inner # return the value 'inner' which is an address

def add(a, b=0):

return a + b #a + b = a + 0 = a

print(id(add)) #address of add in line 10

add = counter(add) # counter(add) return a vlue of inner in line 9, which is an address, add = inner, with a variable count = 0

print(id(add)) # id(add) = id(inner) or it's an address of inner

add(1,1)

add(2,2)

# decorator is used to modify function add. But we don't change the function add, but enhance more things to run

# we add a variable 'count' into function add.

# we don't want to change the functionality of function add, but add additional characteristics into it,