Function In Python For Data Science

             Function In Python For Data Science

                      - Functions ():
    What do you understand by functions ?
        - It performs a predefined task or a formula
        - functions take some value as input and generates 

some value as output  
        - input -> function -> output
        - it is used to reduce our effort when performing same 

task again and again
    - y = f(x) where f(x) = sin(x)
    - Function definition - Here we create a function
    - function call - Here we use the function. It works only when a function is already defined

        - Function definition
    def <function_name>(object1, object2, ...):
         statement_1
         statement_2
         ...
          return object
    - Example - Add two numbers
    def add_numbers(x, y):
         s = x + y
         return s
        a = 5
       b = 10
    print add_numbers(a, b)
  
Key concepts related to function definition and arguments
    - More/less number of inputs to a function than the number   of inputs in the function definition
    def f1(v1, v2, v3):
        .
        .
        return output
    out = f1(5, 10)  # Error - less number of inputs, 3 required,      2 given
    out = f1(5, 10, 15) # No error
    out = f1(5, 10, 15, 20) # Error - More inputs. 3 required, 4        given
   
    - Named arguments as input
    out = f1(v1 = 5, 10, 15)
    out = f1(v1 = 5, v2 = 10, 15)
    out = f1(v1 = 5, v2 = 10, v3 = 15)
    out = f1(v2 = 5, v3 = 10, v1 = 15)
    You can input the value of variables by using the name of      the variable used in function definition
   
    - Default arguments
    def f1(v1, v2, v3=20):
        .
        .
        return output
    out = f1(5, 10)  # No Error. The value of v3 is taken as 20
    out = f1(5, 10, 15) # No error. The value of v3 is now 15
   
      - Function without return statement
    
   def add_numbers(a, b):
        print a+b
    add_numbers(5, 10)  # This will works
    out = add_numbers(5, 10) # This also works, however, the out now contains "None" value