Class and Object Terms

The foundations of Object-Oriented Programming is defining a Class

  • In Object-Oriented Programming (OOP), a class is a blueprint for creating an Object. (a data structure). An Object is used like many other Python variables.
  • A Class has ...
    • a collection of data, these are called Attributes and in Python are pre-fixed using the keyword self
    • a collection of Functions/Procedures. These are called *Methods when they exist inside a Class definition.
  • An Object is created from the Class/Template. Characteristics of objects ...
    • an Object is an Instance of the Class/Template
    • there can be many Objects created from the same Class
    • each Object contains its own Instance Data
    • the data is setup by the Constructor, this is the "init" method in a Python class
    • all methods in the Class/Template become part of the Object, methods are accessed using dot notation (object.method())
  • A Python Class allow for the definition of @ decorators, these allow access to instance data without the use of functions ...
    • @property decorator (aka getter). This enables developers to reference/get instance data in a shorthand fashion (object.name versus object.get_name())
    • @name.setter decorator (aka setter). This enables developers to update/set instance data in a shorthand fashion (object.name = "John" versus object.set_name("John"))
    • observe all instance data (self._name, self.email ...) are prefixed with "", this convention allows setters and getters to work with more natural variable name (name, email ...)

Class and Object Code

# Werkzeug is a collection of libraries that can be used to create a WSGI (Web Server Gateway Interface)
# A gateway in necessary as a web server cannot communicate directly with Python.
# In this case, imports are focused on generating hash code to protect passwords.
from werkzeug.security import generate_password_hash, check_password_hash
import json

# Define a User Class/Template
# -- A User represents the data we want to manage
class User:    
    # constructor of a User object, initializes the instance variables within object (self)
    def __init__(self, name, uid, password):
        self._name = name    # variables with self prefix become part of the object, 
        self._uid = uid
        self.set_password(password)

    # a name getter method, extracts name from object
    @property
    def name(self):
        return self._name
    
    # a setter function, allows name to be updated after initial object creation
    @name.setter
    def name(self, name):
        self._name = name
    
    # a getter method, extracts email from object
    @property
    def uid(self):
        return self._uid
    
    # a setter function, allows name to be updated after initial object creation
    @uid.setter
    def uid(self, uid):
        self._uid = uid
        
    # check if uid parameter matches user id in object, return boolean
    def is_uid(self, uid):
        return self._uid == uid
    
    @property
    def password(self):
        return self._password[0:10] + "..." # because of security only show 1st characters

    # update password, this is conventional setter
    def set_password(self, password):
        """Create a hashed password."""
        self._password = generate_password_hash(password, method='sha256')

    # check password parameter versus stored/encrypted password
    def is_password(self, password):
        """Check against hashed password."""
        result = check_password_hash(self._password, password)
        return result
    
    # output content using str(object) in human readable form, uses getter
    def __str__(self):
        return f'name: "{self.name}", id: "{self.uid}", psw: "{self.password}"'

    # output command to recreate the object, uses attribute directly
    def __repr__(self):
        return f'Person(name={self._name}, uid={self._uid}, password={self._password})'


# tester method to print users
def tester(users, uid, psw):
    result = None
    for user in users:
        # test for match in database
        if user.uid == uid and user.is_password(psw):  # check for match
            print("* ", end="")
            result = user
        # print using __str__ method
        print(str(user))
    return result
        

# place tester code inside of special if!  This allows include without tester running
if __name__ == "__main__":

    # define user objects
    u1 = User(name='Thomas Edison', uid='toby', password='123toby')
    u2 = User(name='Nicholas Tesla', uid='nick', password='123nick')
    u3 = User(name='Alexander Graham Bell', uid='lex', password='123lex')
    u4 = User(name='Eli Whitney', uid='eli', password='123eli')
    u5 = User(name='Hedy Lemarr', uid='hedy', password='123hedy')

    # put user objects in list for convenience
    users = [u1, u2, u3, u4, u5]

    # Find user
    print("Test 1, find user 3")
    u = tester(users, u3.uid, "123lex")


    # Change user
    print("Test 2, change user 3")
    u.name = "John Mortensen"
    u.uid = "jm1021"
    u.set_password("123qwerty")
    u = tester(users, u.uid, "123qwerty")


    # Make dictionary
    ''' 
    The __dict__ in Python represents a dictionary or any mapping object that is used to store the attributes of the object. 
    Every object in Python has an attribute that is denoted by __dict__. 
    Use the json.dumps() method to convert the list of Users to a JSON string.
    '''
    print("Test 3, make a dictionary")
    json_string = json.dumps([user.__dict__ for user in users]) 
    print(json_string)

    print("Test 4, make a dictionary")
    json_string = json.dumps([vars(user) for user in users]) 
    print(json_string)
Test 1, find user 3
name: "Thomas Edison", id: "toby", psw: "sha256$nTQ..."
name: "Nicholas Tesla", id: "nick", psw: "sha256$JPM..."
* name: "Alexander Graham Bell", id: "lex", psw: "sha256$iHV..."
name: "Eli Whitney", id: "eli", psw: "sha256$US0..."
name: "Hedy Lemarr", id: "hedy", psw: "sha256$2cC..."
Test 2, change user 3
name: "Thomas Edison", id: "toby", psw: "sha256$nTQ..."
name: "Nicholas Tesla", id: "nick", psw: "sha256$JPM..."
* name: "John Mortensen", id: "jm1021", psw: "sha256$2I7..."
name: "Eli Whitney", id: "eli", psw: "sha256$US0..."
name: "Hedy Lemarr", id: "hedy", psw: "sha256$2cC..."
Test 3, make a dictionary
[{"_name": "Thomas Edison", "_uid": "toby", "_password": "sha256$nTQxZ9alViZd3WOn$34c90a641520c96e3d91ac148340b8b07d3c0958249dfcfe4a3eb05e2621efef"}, {"_name": "Nicholas Tesla", "_uid": "nick", "_password": "sha256$JPMovUtCRid1pCTE$089368f59621e8878ea730e5328bd9fc442f1d63f40d99f52502c059f9921281"}, {"_name": "John Mortensen", "_uid": "jm1021", "_password": "sha256$2I7yhf1jQOPNu2YE$473f9f24b42cbbd52d6fd4effe03b73ba41ff31ea5532940480aadef56b3ce2d"}, {"_name": "Eli Whitney", "_uid": "eli", "_password": "sha256$US0fsfAaoQix8ido$5b6bac49c74a9fe08b18147a8d0f5c41d7805c42238a9d29dc2e8dbafff8324f"}, {"_name": "Hedy Lemarr", "_uid": "hedy", "_password": "sha256$2cC6Hp5Z4WcmxpBK$df9ed2dbe43edee11d7dc5101057274b2c47be5db95d6610ab7e4fba2dbf6d17"}]
Test 4, make a dictionary
[{"_name": "Thomas Edison", "_uid": "toby", "_password": "sha256$nTQxZ9alViZd3WOn$34c90a641520c96e3d91ac148340b8b07d3c0958249dfcfe4a3eb05e2621efef"}, {"_name": "Nicholas Tesla", "_uid": "nick", "_password": "sha256$JPMovUtCRid1pCTE$089368f59621e8878ea730e5328bd9fc442f1d63f40d99f52502c059f9921281"}, {"_name": "John Mortensen", "_uid": "jm1021", "_password": "sha256$2I7yhf1jQOPNu2YE$473f9f24b42cbbd52d6fd4effe03b73ba41ff31ea5532940480aadef56b3ce2d"}, {"_name": "Eli Whitney", "_uid": "eli", "_password": "sha256$US0fsfAaoQix8ido$5b6bac49c74a9fe08b18147a8d0f5c41d7805c42238a9d29dc2e8dbafff8324f"}, {"_name": "Hedy Lemarr", "_uid": "hedy", "_password": "sha256$2cC6Hp5Z4WcmxpBK$df9ed2dbe43edee11d7dc5101057274b2c47be5db95d6610ab7e4fba2dbf6d17"}]

Hacks

Add new attributes/variables to the Class. Make class specific to your CPT work.

  • Add classOf attribute to define year of graduation
    • Add setter and getter for classOf
  • Add dob attribute to define date of birth
    • This will require investigation into Python datetime objects as shown in example code below
    • Add setter and getter for dob
  • Add instance variable for age, make sure if dob changes age changes
    • Add getter for age, but don't add/allow setter for age
  • Update and format tester function to work with changes

Start a class design for each of your own Full Stack CPT sections of your project

  • Use new code cell in this notebook
  • Define init and self attributes
  • Define setters and getters
  • Make a tester

Start Code for Hacks

from datetime import date

def calculate_age(born):
    today = date.today()
    return today.year - born.year - ((today.month, today.day) < (born.month, born.day))

dob = date(2004, 12, 31)
age = calculate_age(dob)
print(age)
18
class Student:
    def __init__(self, name, major, gpa, classOf):
        self.name = name
        self.major = major
        self.gpa = gpa
        self.classOf = classOf
        self.dob = None
        self.age = None

    def set_dob(self, dob):
        self.dob = dob
        self.age = self.calc_age()

    def calc_age(self):
        today = date.today()
        age = today.year - self.dob.year - ((today.month, today.day) < (self.dob.month, self.dob.day))
        return age

    def get_classOf(self):
        return self.classOf

    def get_age(self):
        return self.age


def tester():
    student1 = Student("Aniket", "Programmer", 4.2, 2025)
    student1.set_dob(date(2007, 2, 20))
    print("Student's name is: " + student1.name)
    print("Student's class of: " + str(student1.get_classOf()))
    print("Student's age is: " + str(student1.get_age()) + " years old")

tester()
Student's name is: Aniket
Student's class of: 2025
Student's age is: 15 years old
class Food:
    def __init__(self, name, price, ingredients):
        self.name = name
        self.price = price
        self.ingredients = ingredients
    
    # getters
    def get_name(self):
        return self.name

    def get_price(self):
        return self.price

    def get_ingredients(self):
        return self.ingredients

    # setters
    def set_name(self, name):
        self.name = name

    def set_price(self, price):
        self.price = price

    def set_ingredients(self, ingredients):
        self.ingredients = ingredients

# tester
burger = Food("Hamburger", 5.99, ["Bun", "Beef Patty", "Lettuce", "Tomato", "Onion"])

print("Item name:", burger.get_name())
print("The price is:")
print(burger.get_price())
print("The ingredients are:")
print(*burger.get_ingredients())
Item name: Hamburger
The price is:
5.99
The ingredients are:
Bun Beef Patty Lettuce Tomato Onion