Model and Object-Oriented Programming
Object Oriented Programming is a part of learning Python. The objective of this blog is to introduce OOP with the intention of PBL task to create a database. The foundations for a database is defining a Class and understanding instance data and methods. A database is often a focus of backend coding as it will store persistent data, that can be recalled after the immediate session is closed.
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 ...)
# 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
# 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)
Hacks
Add new attributes/variables to the Class.
- 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
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)
from werkzeug.security import generate_password_hash, check_password_hash
from datetime import date
import json
class User:
def __init__(self, name, uid, password, dob, classOf):
self._name = name # variables with self prefix become part of the object,
self._uid = uid
self.set_password(password)
self._dob = dob
self._classOf = classOf
@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
# dob property is returned as string, to avoid unfriendly outcomes
@property
def dob(self):
dob_string = self._dob.strftime('%m-%d-%Y')
return dob_string
# dob should be have verification for type date
@dob.setter
def dob(self, dob):
self._dob = dob
# age is calculated and returned each time it is accessed
@property
def age(self):
today = date.today()
return today.year - self._dob.year - ((today.month, today.day) < (self._dob.month, self._dob.day))
#class of getter
@property
def classOf(self):
return self._classOf
#class of setter
@classOf.setter
def classOf(self, classOf):
self._classOf = classOf
# dictionary is customized, removing password for security purposes
@property
def dictionary(self):
dict = {
"name" : self.name,
"uid" : self.uid,
"dob" : self.dob,
"age" : self.age,
"class_of": self.classOf
}
return dict
# 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 json dumps, this is ready for API response
def __str__(self):
return json.dumps(self.dictionary)
# output command to recreate the object, uses attribute directly
def __repr__(self):
return f'User(name={self._name}, uid={self._uid}, password={self._password},dob={self._dob}, class_of={self._classOf})'
if __name__ == "__main__":
u1 = User(name="Aaron Rubin", uid="Aaronrub", password="abc1234", dob=date(2007,11,5), classOf="2025")
print(u2)
class Stock:
def __init__(self, name, ticker, price):
# constructor method, called when an object of the class is created
# initializes the object's attributes (name, ticker, price) with the input values
self.name = name
self.ticker = ticker
self.price = price
def update_price(self, new_price):
# method to update the price attribute of the object
self.price = new_price
def print_profile(self):
# method to print the object's attributes
print("Name: ", self.name)
print("Ticker: ", self.ticker)
print("Price: ", self.price)
# remove 'import stock'
# creating an object of the Stock class
stock = Stock("Google", "GOOGL", 1500)
# calling the print_profile method on the object to print its attributes
stock.print_profile()
# Output: Name: Google, Ticker: GOOGL, Price: 1500
# calling the update_price method on the object to update its price attribute
stock.update_price(1550)
# calling the print_profile method on the object to print its updated attributes
stock.print_profile()
# Output: Name: Google, Ticker: GOOGL, Price: 1550
# Import the ipywidgets library
import ipywidgets as widgets
# Create a text box for the user to input the name of the stock
name_input = widgets.Text(description='Name:')
# Create a text box for the user to input the ticker of the stock
ticker_input = widgets.Text(description='Ticker:')
# Create a text box for the user to input the price of the stock
price_input = widgets.Text(description='Price:')
# Create a button that, when clicked, creates a stock object and displays its attributes
create_button = widgets.Button(description='Create Stock')
# Create a function that is called when the create_button is clicked
def create_stock(b):
# Get the values entered in the input boxes
name = name_input.value
ticker = ticker_input.value
price = price_input.value
# Create a stock object using the input values
stock = Stock(name, ticker, price)
# Display the stock's attributes
stock.print_profile()
# Tell the create_button to call the create_stock function when clicked
create_button.on_click(create_stock)
# Display the input boxes and button
widgets.VBox([name_input, ticker_input, price_input, create_button])
import ipywidgets as widgets
# Create a text box for the user to input the name of the stock
name_input = widgets.Text(description='Name:')
# Create a text box for the user to input the ticker of the stock
ticker_input = widgets.Text(description='Ticker:')
# Create a text box for the user to input the price of the stock
price_input = widgets.Text(description='Price:')
# Create a button that, when clicked, creates a stock object and displays its attributes
create_button = widgets.Button(description='Create Stock')
# Create a function that is called when the create_button is clicked
def create_stock(b):
# Get the values entered in the input boxes
name = name_input.value
ticker = ticker_input.value
price = price_input.value
# Create a stock object using the input values
stock = Stock(name, ticker, price)
# Display the stock's attributes
stock.print_profile()
# Tell the create_button to call the create_stock function when clicked
create_button.on_click(create_stock)
# Display the input boxes and button
widgets.VBox([name_input, ticker_input, price_input, create_button])