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3: The Function Object
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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
-----------------------------

.. code-block:: python

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

A Way to think of a function Definition
------------------------------------------

.. code-block:: python

    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
---------------------

.. code-block:: python

    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
------------------------------

.. code-block:: python

    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

.. code-block:: python

    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

.. literalinclude:: programs/passByObject.py
   :language: python

.. literalinclude:: programs/functions.py
   :language: python