In previous Chapter, I presented

• Function
  • A Function is defined as a piece of Code (or block of Python Statements) to perform a specific Programming Task
• Python Program 
  • A Python Program is a collection of one or more Functions
• Main Components of a Function 
  • The three main components of a Function are
    • Function Prototype
    • Function Definition 
    • Function Call
• Function Prototype
  • A Function Prototype is a function declaration that specifies the data types of its arguments in the parameter list 
  • Functions can be declared implicitly by their appearance in a call. Arguments to functions undergo the default conversions before the call. The number and type of arguments are not checked
• Function Prototype
  • Function Prototype comprises of three parts
    • Return Type
    • Function Name
    • List of Arguments / Parameters
• Four Variations in Function Prototype
  • No Return Type, No Arguments / Parameters 
  • No Return Type, Arguments / Parameters 
  • Return Type, No Arguments / Parameters 
  • Return Type, Arguments / Parameters 
• Types of Functions 
  • There are two types of Functions in Python
    • Built-in Functions 
    • User Defined Functions 
• Built-in Function
  • A Built-in Function is defined as a Function whose functionality is pre-defined in Python Programming Language 
• User Defined Functions
  • A User Defined Function is defined as a Function that you can define yourself in Python Programming Language 
• Function Definition 
  • Function Definition is made up of two parts
    • Function Header
    • Body of Function 
• Scope of Variable
  • The scope of the variable is simply lifetime of a variable. It is block of code under which a variable is applicable or alive
• Types of Scope of Variable
  • There Variables can be declared in two ways:
    • Local Variable (Inside a function or a block)
    • Global Variable (Outside of all functions)
  • In the definition of function parameters which are called formal parameters
• Local Variables
  • The Variables that are declared inside a function / subroutine are called Local Variables
• Global Variables
  • The Variables that are declared outside a function / subroutine are called Global Variables
• Formal Parameters
  • Formal parameters, are treated as local variables with-in a function and they take precedence over global variables
• Pass Object by Value and Pass Object by Reference
  • An immutable object’s value cannot be changed, even if it is passed a new value
• Passing by value refers to passing a copy of the value
  • Passing by reference refers to passing the real reference of the variable in memory