A class on object-oriented python for beginners.

1. Object Oriented
Python
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2. Object Oriented
Python
The way programming was meant to be
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3. Who we are
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4. Who we are
Anna
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5. Who we are
David Anna
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6. Why do I care about
classes?
• Code organization
• Readability
• Making large-scale changes easier
• What everybody does these days
• Encapsulation (SAT word!)
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7. What is a class?
Factory for creating nouns
based on your description
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8. What is a class?
Factory for creating nouns
based on your description
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9. What does an object
contain?
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10. What does an object
contain?
Local Data
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11. What does an object
contain?
Local Data
Name: David
Birthday: Dec 18
Job: Software Engineer
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12. What does an object
contain?
Local Data
Name: David
Birthday: Dec 18
Job: Software Engineer
Actions
say_hello()
eat_spaghetti()
teach_a_class()
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13. What does an object
contain?
Local Data Local Data
Name: David Name: Anna
Birthday: Dec 18 Birthday: Sep 6
Job: Software Engineer Job: Entrepreneur
Actions
say_hello()
eat_spaghetti()
teach_a_class()
Tuesday, April 24, 12

14. What does an object
contain?
Local Data Local Data
Name: David Name: Anna
Birthday: Dec 18 Birthday: Sep 6
Job: Software Engineer Job: Entrepreneur
Actions
say_hello()
eat_spaghetti()
teach_a_class()
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15. Syntax
Definition
class User(object):
name = "Jack"
birthday = "Jan 2"
job = "student"
def say_hello(self):
print "Hello, I'm " + self.name
def eat_spaghetti(self):
print "Yum!"
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16. Syntax
Definition Usage
>>> jack1 = User()
class User(object):
>>> print jack1.name
name = "Jack"
"Jack"
birthday = "Jan 2"
job = "student"
>>> jack2 = User()
>>> print jack2.name
def say_hello(self):
"Jack"
print "Hello, I'm " + self.name
>>> jack1.say_hello()
def eat_spaghetti(self):
"Hello, I'm Jack"
print "Yum!"
>>> jack2.eat_spaghetti()
"Yum!"
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17. Syntax
Definition Usage
>>> jack1 = User()
class User(object):
>>> print jack1.name
name = "Jack"
"Jack"
birthday = "Jan 2"
job = "student"
>>> jack2 = User()
>>> print jack2.name
def say_hello(self):
"Jack"
print "Hello, I'm " + self.name
>>> jack1.say_hello()
def eat_spaghetti(self):
"Hello, I'm Jack"
print "Yum!"
>>> jack2.eat_spaghetti()
"Yum!"
One class, multiple objects
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18. Local Data
class User(object): >>> harry = User("Harry")
def __init__(self, name): >>> sally = User("Sally")
self.name = name >>> harry.say_hello()
"Hello, I'm Harry"
def say_hello(self): >>> sally.say_hello()
print "Hello, I'm " + self.name "Hello, I'm Sally"
>>> harry.greet(sally)
def greet(self, other): "Hi Sally, I'm Harry!"
print "Hi " + other.name + ", " + >>> sally.greet(harry)
"I'm " + self.name + "!" "Hi Harry, I'm Sally!"
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19. Local Data
class User(object): >>> harry = User("Harry")
def __init__(self, name): >>> sally = User("Sally")
self.name = name >>> harry.say_hello()
"Hello, I'm Harry"
def say_hello(self): >>> sally.say_hello()
print "Hello, I'm " + self.name "Hello, I'm Sally"
>>> harry.greet(sally)
def greet(self, other): "Hi Sally, I'm Harry!"
print "Hi " + other.name + ", " + >>> sally.greet(harry)
"I'm " + self.name + "!" "Hi Harry, I'm Sally!"
>>> harry.name = "Frank"
>>> harry.say_hello()
"Hello, I'm Frank!"
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20. Banking Program
Objects we’ll need:
• Banks
• Users
• Accounts
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21. Main Program
• program:
•bank classbank object.method.
create
• create create user object.
with log in
•user class with name & password
• create log in.
•account class with amount
• create create account object.
•
• add money.
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22. Main Program
• program:
•bank classbank object.method.
create
• create create user object.
with log in
•user class with name & password
• create log in.
•account class with amount
• create create account object.
•
• add money.
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23. Classes & Objects
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24. Bank Class
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25. User Class
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26. Account Class
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27. Tuesday, April 24, 12

28. Main Program
• program:
• create bank object.
• create user object.
• log in.
• create account object.
• add money.
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29. Main Program
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30. Main Program
• program:
•bank classbank object.method.
create
• create create user object.
with log in
•user class with name & password
• create log in.
•account class with amount
• create create account object.
•
• add money.
Tuesday, April 24, 12

31. Main Program
• program:
•bank classbank object.method.
create
• create create user object.
with log in
•user class with name & password
• create log in.
•account class with amount
• create create account object.
•
• add money.
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32. Bank Class
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33. Tuesday, April 24, 12

34. Main Program
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35. What if changes
need to be made?
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36. Banking Example
>>> bank = Bank()
>>> account_alice = Account(bank)
>>> account_alice.deposit(200)
>>> account_bob = Account(bank)
>>> account_bob.deposit(250)
>>> account_carol = Account(bank)
>>> account_carol.deposit(100)
account_alice.balance: 200
account_bob.balance: 250
account_carol.balance: 100
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37. Banking Example
>>> bank = Bank()
>>> account_alice.deposit(100)
>>> account_alice = Account(bank)
>>> account_bob.deposit(50)
>>> account_alice.deposit(200)
>>> account_carol.withdraw(60)
>>> account_bob = Account(bank)
>>> account_alice.withdraw(200)
>>> account_bob.deposit(250)
>>> account_carol.deposit(200)
>>> account_carol = Account(bank)
>>> account_bob.withdraw(80)
>>> account_carol.deposit(100)
account_alice.balance: 100
account_bob.balance: 220
account_carol.balance: 240
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38. Changes!
The government has just declared that
all bank deposits will be taxed %5.
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39. Changes!
The government has just declared that
all bank deposits will be taxed %5.
Oh no!
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40. Changes!
The government has just declared that
all bank deposits will be taxed %5.
Oh no!
Do we have to rewrite our entire program?
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41. Changes!
The government has just declared that
all bank deposits will be taxed %5.
Oh no!
Do we have to rewrite our entire program?
Nope!
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42. Original Version
class Account(object):
balance = 0
def deposit(self, amount):
self.balance = self.balance + amount
def withdraw(self, amount):
self.balance = self.balance - amount
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43. New Version
class Account(object):
balance = 0
def deposit(self, amount):
tax = amount * 5/100
remaining = amount - tax
self.balance = self.balance + remaining
def withdraw(self, amount):
self.balance = self.balance - amount
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44. Still Works
>>> bank = Bank()
>>> account_alice.deposit(100)
>>> account_alice = Account(bank)
>>> account_bob.deposit(50)
>>> account_alice.deposit(200)
>>> account_carol.withdraw(60)
>>> account_bob = Account(bank)
>>> account_alice.withdraw(200)
>>> account_bob.deposit(250)
>>> account_carol.deposit(200)
>>> account_carol = Account(bank)
>>> account_bob.withdraw(80)
>>> account_carol.deposit(100)
account_alice.balance: 95
account_bob.balance: 218.50
account_carol.balance: 230
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45. Any questions?
Classes? Methods?
Objects?
Syntax?
Local data?
Tuesday, April 24, 12