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Computer Programming: Object-Oriented Programming and Functions

Object-Oriented Programming (OOP)

  • We are really only going to scratch the surface of OOP in this exercise
  • OOP is a complex programming paradigm that can't be mastered in a single setting
  • But, we can cover the basics to allow you to explore further

Classes

  • Serve as a template from which to build objects
  • Think of it as a blueprint: design first, then build
  • We can modify the blueprint to add features as needed

Objects

  • Objects are instantiated from classes
  • An object inherits its properties and methods from its class
Classes and Objects in PowerShell 
# Define a "Person" class
# We must explicitly set the data types for any class properties or methods
class Person {
    [String]$FirstName
    [String]$LastName
    [String]$EyeColor
    [Int]$Age
    [String[]]$Nicknames

    # Eat method
    # [String] on the left indicates the output from the method
    # [String]$Food indicates Eat() takes a string argument to the $Food parameter
    [String] Eat([String]$Food) {
    	return "That $Food was delicious!"
    }
    
    # Walk method
    # [String] on the left indicates the output from the method
    # [Int]$Steps indicates Eat() takes an integer argument to the $Steps parameter
    [String] Walk([Int]$Steps) {
    	return "I walked $Steps steps."
    }
    
    # Sleep method
    # [Void] indicates this method produces no output
    [Void] Sleep() {
    	Start-Sleep -Seconds 10
    }
}

# Create a new "Person" object from the class
# It has inherited its properties and methods from said class
# Assign values to the properties
$johnDoe = New-Object Person
$johnDoe.FirstName = 'John'
$johnDoe.LastName = 'Doe'
$johnDoe.EyeColor = 'Brown'
$johnDoe.Age = 33
$johnDoe.Nicknames = @('johnny', 'jim', 'anonymous')

# Print the object to output
$johnDoe

# Feed John Doe
# The Eat method takes a string
$johnDoe.Eat('spaghetti')

# John Doe needs a walk
# The Walk method take an integer
$johnDoe.Walk(10000)

# John Doe needs a nap
# The Sleep method does not take input
$johnDoe.Sleep()

 

Classes and Objects in Python 
import time

# Unlike PowerShell, we do not declare data types
class Person:
    def __init__(self):
        self.FirstName = ""
        self.LastName = ""
        self.EyeColor = ""
        self.Age = 0
        self.Nicknames = []

    # Eat method
    def Eat(self, food):
        return f"That {food} was delicious!"

    # Walk method
    def Walk(self, steps):
        return f"I walked {steps} steps."

    # Sleep method
    def Sleep(self):
        time.sleep(10)

# Create a new "Person" object from the class
# It has inherited its properties and methods from the class
# Assign values to the properties
johnDoe = Person()
johnDoe.FirstName = 'John'
johnDoe.LastName = 'Doe'
johnDoe.EyeColor = 'Brown'
johnDoe.Age = 33
johnDoe.Nicknames = ['johnny', 'jim', 'anonymous']

# Print the object to output
print(vars(johnDoe))

# Feed John Doe
# The Eat method takes a string
print(johnDoe.Eat('spaghetti'))

# John Doe needs a walk
# The Walk method takes an integer
print(johnDoe.Walk(10000))

# John Doe needs a nap
# The Sleep method does not take input
johnDoe.Sleep()

 

Functional Programming

  • Good code is DRY code, Don't Repeat Yourself
    • If you find yourself repeating the same lines of code, it's time to stop and refactor
    • Why is code that repeats bad?
      • If you update a code block in one section, but forget to update that same code block in another section, then you're creating bugs in the code
    • Code that is not DRY is difficult to maintain
  • The point of functions is to allow you to write once, reference many
    • Write the function and use it where it's needed

Example of Non-Dry Code

PowerShell

PowerShell Non-Dry Code Solution 
$int1 = 1
$int2 = 10
$product = $int1 * $int2
Write-Host "The product is: $product"

$int1 = 2
$int2 = 15
$product = $int1 * $int2
Write-Host "The product is: $product"

$int1 = 10
$int2 = 33
$product = $int1 * $int2
Write-Host "The product is: $product"

This code could be improved with the use of a function. It may seem like more work, but we now have a function that we can call repeatedly any time we need to find the product of two integers.

function Get-ProductOfIntegers {
  
  [CmdletBinding()]
  Param (
    [Parameter(Mandatory = $true, Position = 0)]
    [Int]$Integer1,
    
    [Parameter(Mandatory = $true, Position = 1)]
    [Int]$Integer2
  )
  
  try {
    return $Integer1 * $Integer2
  }
  catch {
    throw $_
  }
  
}

Get-ProductOfIntegers -Integer1 10 -Integer2 100
Get-ProductOfIntegers -Integer1 12 -Integer2 55
Get-ProductOfIntegers -Integer1 333 -Integer2 33


Python

Python Non-Dry Code Solution 
int1 = 1
int2 = 10
product = int1 * int2
print(f"The product is: {product}")

int1 = 2
int2 = 15
product = int1 * int2
print(f"The product is: {product}")

int1 = 10
int2 = 33
product = int1 * int2
print(f"The product is: {product}")

This code could be improved with the use of a function. It may seem like more work, but we now have a function that we can call repeatedly any time we need to find the product of two integers.

def get_product(integer1, integer2):
    try:
        # With PowerShell, we can do the validation on user input in the parameter block
        # With Python, we need to validate the input here
        if not isinstance(integer1, int) or not isinstance(integer2, int):
            raise ValueError("Please provide two integers")
        else:
            return int(integer1) * int(integer2)
    except Exception as e:
        raise e

print(get_product(1, 10))
print(get_product(33, 33))

Creating Well-Designed Functions

  • A function is a tool that should repeatedly do one thing well
  • It should also be idempotent

  • Idempotency means that every time the function receives an input, it should process it the same every single time. That may mean the function returns a consistent output or it returns a consistent error.

  • Just as a screwdriver was intended for a specific purpose, so too should your functions be focused on a single task
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