3: The Function Object

Summary

• Functions is Python are objects and can be used anywhere an object can

• You can pass a function as a parameter and return a function result

• Function parameters are passed by object reference, which means changes to parameters do not affect the variables used as arguments

• Function s can have attributes defined which have a lifetime beyond that oof the functions local variables

• Local variables exist only while the function is being executed, but attributes exist as long as the function object does

• Lambda expressions are lightweight ways of creating function objects. They simplify the syntax for passing function arguments

• Functions have variables which reference them rather than names

• Functions can refer to their own attributes in code

• A function object is an example of a callable

Functions as Objects

Python Function Definition

def sum(a,b):
    c = a + b
    return c

A Way to think of a function Definition

sum = def(a,b):
    c = a + b
    return c

# invalid syntax but shows that the variable "sum" is created with a reference to the new function object

Function attributes

def sum(a,b):
    c = a + b
    return c

#A function object has many predefined attributes that can be useful and you can add new attributes to a function object and make use of them

sum.myAttribute = 1
print(sum.myAttribute)

Why Functions are Objects

def math(f,a,b):  #first parameter 'f" is a reference to a unction
    return f(a,b)

def sum(a,b):
    c = a + b
    return c

def sub(a,b):
    c = a - b
    return c

print(math(sum,1,2))
print(math(sub,1,2))

Function Self Reference

Attributes are a great way to store state information for the function

This function counts the the number of times it has been used

def myFunction():
    myFunction.count =+ 1

myFunction.count = 0

print(myFunction.count) # zero it has not been used yet
myFunction()
print(myFunction.count) # 1 it has been used once etc, etc

Programs

I have attached 2 programs that work with functions and compliment the programs showed above

class myClass1:
    a = 1
class myClass2:
    a = 2

def myFunction(x):
    x = myClass2
    print(x.a) #reference was copied into the function. 2 should be printed

y = myClass1
myFunction(y)
print(y.a) #y remains unchanged by the function and should print 1

##################################################################################
print("-------------------------------------------------------")
#changing the program function slightly means that the function can change things in the calling program

def myFunction2(x):
    x.a = 42       # the attributes of the object the calling program references can be changed
    print(x.a)

z = myClass1
myFunction2(z)
print(z.a)

def sum(a,b):
    c = a + b
    return c
    

#A function object has many predefined attributes that can be useful and you can add new attributes to a function object and make use of them

sum.myAttribute = 1
print(sum.myAttribute)



#Why are functions objects

def math(f,a,b):  #first parameter 'f" is a reference to a function
    return f(a,b)

def sum(a,b):
    c = a + b
    return c

def sub(a,b):
    c = a - b
    return c

print(math(sum,1,2))
print(math(sub,1,2))