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CSE 160 Section 8

Classes!

CSE 160: Classes

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Logistics

  • Written check-in 8 due Friday Feb 27

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  • Programming Practice 8 due Wed Mar 04
    • Wait for autograder!

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  • HW5 due Fri Mar 13 - No Resubmissions

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CSE 160: Classes

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Classes

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What is a Class?

A class encapsulates and abstracts data and logic that you can use in your programs

We want to make a program that can keep track of phone numbers.

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CSE 160: Classes

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Classes vs. Objects

A class is a blueprint- it defines what data and behavior an object will have

We can create an object instance from a class

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Class

Multiple object instances

CSE 160: Classes

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A Class Contains…

Variables / fields to hold the necessary data

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A phone number should probably store:

  • Area code
  • Exchange
  • Number

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A Class Also Contains…

Methods/behaviors to create, query, and modify an instance of a class

(Methods are basically functions inside classes)

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A phone number should probably be able to:

  • Be created
  • Be called
  • Print its number

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CSE 160: Classes

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Creating an Instance of A Class

When we want to start using a class, we typically want to set some its variables to their correct values

This is done through a special method called __init__

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When we create a phone number, we want to specify it’s area code, exchange, and number.

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CSE 160: Classes

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CSE 160: Classes

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CSE 160: Classes

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Problem 1

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Problem 1a

What would the following client code print?

flower_shop = Shop(“Swansons”)

flower_shop.add_item(“Daisy”)

flower_shop.print_inventory()

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Problem 1a

What would the following client code print?

flower_shop = Shop(“Swansons”)

flower_shop.add_item(“Daisy”)

flower_shop.print_inventory()

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Output:

Daisy 1

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Problem 1b

What code would you write to make a new shop called Arcane Comics that has 5 comics in it, and then print out it's inventory?

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Problem 1b

What code would you write to make a new shop called Arcane Comics that has 5 comics in it, and then print out it's inventory?

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comic_shop = Shop("Arcane Comics")

for i in range(5):

comic_shop.add_item("Comic")

comic_shop.print_inventory()

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Problem 1c

Adding one item at a time is extremely tedious. Write a function for the class Shop called add_items that given an item and an amount, adds that amount to the store's inventory.

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Problem 1c

Adding one item at a time is extremely tedious. Write a function for the class Shop called add_items that given an item and an amount, adds that amount to the store's inventory.

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def add_items(self, item, amount):

if item not in self.inventory:

self.inventory[item] = 0

self.inventory[item] += amount

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Problem 2

Given the doc-strings and example output, fill in the code for each method in the StreamingService class.

CSE 160: Classes

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Problem 2

Given the doc-strings and example output, fill in the code for each method in the StreamingService class.

Python Tutor

CSE 160: Classes