python-sql-lessons/python/lessons/python_2.md

Intro to Python pt. 2

Lesson Objectives

1. Get user input
2. Repeatedly perform a set of commands
3. Use a for loop
4. Define a function
5. Create a class for an object
6. Have a class inherit from another
7. Create a factory for objects

Get user input

You can get user input from the command like so:

user_input = input("Please enter your name: ")
print("Hello, " + user_input + "!")

Repeatedly perform a set of commands

a = 10
while a < 20:
    print("the value of a is currently: " + str(a))
    a += 1

ACTIVITY

1. Write a program that models this flow chart:

   

Use a for loop

The process of looping through an array can be simplified with a for loop:

foods = ['hot dogs', 'beer', 'bald eagles']
for food in foods:
    print(food)

You can loop through a set of numbers using a range

for x in range(0, 3):
  print(x)

ACTIVITIES

1. Given the following list [70, 95, 97, 55, 3, 24, 89, 97, 84, 11]

   • Write a program that loops through each value in the list and prints it
   • Write a program that loops through each value in the list and adds them all together
   • Write a program that loops through each value in the list and prints the average
   • Write a program that loops through each value in the list and prints the minimum
   • Write a program that loops through each value in the list and prints the maximum

2. Combine all the programs from the previous step into one program that asks the user what operation they would like to do

3. Alter the last program so that it performs the operations for only numbers that are greater than a number specified by the user

Define a function

If you have a routine that you run over and over again, you can define your own function:

def greet():
  print('hi')

greet()

Functions can take parameters which alter their functionality:

def greet(name):
  print('hi, ' + name)

greet('bob')

Functions can return values:

def add(value1, value2):
  return value1 + value2

print(add(1,3))

ACTIVITIES

Create a calculator program that continually asks a user what operations they want to perform, until the user says 'quit'

Create a class for an object

You can use a class or blueprint for objects that you'll use

class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

  def greet(self):
    print("Hello, my name is " + self.name + ". My age is " + str(self.age))

me = Person("Hunter", 29)
me.greet()
sally = Person("Sally", 53)
sally.greet()

• __init__ is a function that gets called when a new object is created. Make sure you use two underscores on either side of the init or it will break!
• self is the object that's created

Have a class inherit from another

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def greet(self):
        print("Hello, my name is " + self.name + ". My age is " + str(self.age))

    def work(self):
        print("Boring...")

class SuperHero(Person): # tell it to inherit from Person
    def __init__(self, name, age, powers):
        super().__init__(name,age) # call Person's __init__()
        self.powers = powers

    def greet(self):
        super().greet() # call Person's greet()
        self.listPowers()

    def listPowers(self):
        for power in self.powers:
            print(power)

    def work(self): # override Person's work()
        print("To action!")

superman = SuperHero('Clark Kent', 200, ['flight', 'strength', 'invulnerability'])

superman.greet()
superman.work()

Create a factory for objects

class Car:
    def __init__(self, maker, model, serial):
        self.maker = maker
        self.model = model
        self.serial = serial

class CarFactory:
    def __init__(self, name):
        self.name = name
        self.cars = []

    def makeCar(self, model):
        self.cars.append(Car(self.name, model, len(self.cars)))

    def listCars(self):
        for car in self.cars:
            print(car.maker + " " + car.model + " serial#: " + str(car.serial))

    def findCar(self, serial):
        for car in self.cars:
            if(car.serial == serial):
                return car

toyota = CarFactory('Toyota')
toyota.makeCar('Prius')
toyota.makeCar('Rav 4')
toyota.listCars()
print(toyota.findCar(1).model)