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Agenda

0 ) Administrivia

1 ) Dictionaries

2 ) OOP

3 ) Inheritance

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Administrivia

HW 05 due tonight 3/8
Lab 06 due tonight 3/8
Ants due next Thursday 3/14
Midterm 2 coming up!

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Dictionaries

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Dictionaries

dictionaries: data structure that maps key to values

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

Strings, numbers, tuples, etc

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

Strings, numbers, tuples, etc
NOT lists, dictionaries

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

Strings, numbers, tuples, etc
NOT lists, dictionaries

keys-value pairs are not ordered in any specific order

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

Strings, numbers, tuples, etc
NOT lists, dictionaries

keys-value pairs are not ordered in any specific order
dictionaries are mutable!

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

Strings, numbers, tuples, etc
NOT lists, dictionaries

keys-value pairs are not ordered in any specific order
dictionaries are mutable!

can add, remove, modify key-value pairs

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

Strings, numbers, tuples, etc
NOT lists, dictionaries

keys-value pairs are not ordered in any specific order
dictionaries are mutable!

can add, remove, modify key-value pairs
Q: What happens if want to insert a new value for a key that already exists?

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Dictionaries

dictionaries: data structure that maps key to values
keys must be unique and immutable types

Strings, numbers, tuples, etc
NOT lists, dictionaries

keys-value pairs are not ordered in any specific order
dictionaries are mutable!

can add, remove, modify key-value pairs
Q: What happens if want to insert a new value for a key that already exists?
A: The old value gets overridden since all keys are unique! Cannot have two key-value pairs with the same key.

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Dictionary Methods

d[k] = val

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Dictionary Methods

d[k] = val

adds value val to corresponding key k to dictionary d, or replaces old value with new value val to existing key k

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Dictionary Methods

d[k] = val

adds value val to corresponding key k to dictionary d, or replaces old value with new value val to existing key k

del d[k]

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Dictionary Methods

d[k] = val

adds value val to corresponding key k to dictionary d, or replaces old value with new value val to existing key k

del d[k]

removes dictionary value associated with key k

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Dictionary Methods

d[k] = val

adds value val to corresponding key k to dictionary d, or replaces old value with new value val to existing key k

del d[k]

removes dictionary value associated with key k

d.pop(k)

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Dictionary Methods

d[k] = val

adds value val to corresponding key k to dictionary d, or replaces old value with new value val to existing key k

del d[k]

removes dictionary value associated with key k

d.pop(k)

removes key-value pair with key k, and returns the associated value

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Iterating Through Contents of

a Dictionary

2 ways to iterate through a dictionary’s keys

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Iterating Through Contents of

a Dictionary

2 ways to iterate through a dictionary’s keys

for key in dictionary:
for key in dictionary.keys():

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Iterating Through Contents of

a Dictionary

2 ways to iterate through a dictionary’s keys

for key in dictionary:
for key in dictionary.keys():

iterate through a dictionary’s values

for key in dictionary.values():

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Iterating Through Contents of

a Dictionary

2 ways to iterate through a dictionary’s keys

for key in dictionary:
for key in dictionary.keys():

iterate through a dictionary’s values

for key in dictionary.values():

iterate through a dictionary’s key and values

for key, value in dictionary.items():

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Object Oriented Programming

(OOP)

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OOP Goal

Treat data as objects, like in real-life

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OOP Terminology

class: a template for creating objects

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OOP Terminology

class: a template for creating objects

Student, Professor

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

anita = Student(“Anita”, “Junior”, “CS”)

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

anita = Student(“Anita”, “Junior”, “CS”)

instance attribute: a property of an object specific to (belongs to) an instance

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

anita = Student(“Anita”, “Junior”, “CS”)

instance attribute: a property of an object specific to (belongs to) an instance

name, year, major → anita.name is “Anita”

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

anita = Student(“Anita”, “Junior”, “CS”)

instance attribute: a property of an object specific to (belongs to) an instance

name, year, major → anita.name is “Anita”

class attribute: a property of an object that is shared by all instances of the same class

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

anita = Student(“Anita”, “Junior”, “CS”)

instance attribute: a property of an object specific to (belongs to) an instance

name, year, major → anita.name is “Anita”

class attribute: a property of an object that is shared by all instances of the same class

Student.professor → dan_garcia

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

anita = Student(“Anita”, “Junior”, “CS”)

instance attribute: a property of an object specific to (belongs to) an instance

name, year, major → anita.name is “Anita”

class attribute: a property of an object that is shared by all instances of the same class

Student.professor → dan_garcia

method: a function/action that all instances of a class can perform

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OOP Terminology

class: a template for creating objects

Student, Professor

instance: a single object created from a class using its constructor

anita = Student(“Anita”, “Junior”, “CS”)

instance attribute: a property of an object specific to (belongs to) an instance

name, year, major → anita.name is “Anita”

class attribute: a property of an object that is shared by all instances of the same class

Student.professor → dan_garcia

method: a function/action that all instances of a class can perform

watchLecture(), doHomework(), takeExam()

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Method vs. Function

method: function encapsulated by a class

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Method vs. Function

method: function encapsulated by a class
function: routine defined outside of a class

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Important Notes!

The instance specified is passed in implicitly as self

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Mini Quiz!

class Student:

def __init__(self, name):

self.name = name

def attend_lecture(self, subject):

print(self.name + “ is learning about “ + subject)

anita = Student(“Anita”)

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Mini Quiz!

Q: Which of these are valid method calls?

> anita.attend_lecture(“OOP”)

> anita.attend_lecture(anita, “OOP”)

> Student.attend_lecture(“OOP”)

> Student.attend_lecture(anita, “OOP”)

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Mini Quiz!

Q: Which of these are valid method calls?

> anita.attend_lecture(“OOP”)

> anita.attend_lecture(anita, “OOP”)

> Student.attend_lecture(“OOP”)

> Student.attend_lecture(anita, “OOP”)

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Mini Quiz!

Q: Which of these are valid method calls?

> anita.attend_lecture(“OOP”)

> anita.attend_lecture(anita, “OOP”)

attend_lecture takes 2 arguments, but this call passes in 3 arguments! What are the 3 arguments?

> Student.attend_lecture(“OOP”)

> Student.attend_lecture(anita, “OOP”)

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Mini Quiz!

Q: Which of these are valid method calls?

> anita.attend_lecture(“OOP”)

> anita.attend_lecture(anita, “OOP”)

attend_lecture takes 2 arguments, but this call passes in 3 arguments! What are the 3 arguments?

> Student.attend_lecture(“OOP”)

No specific instance for this method was given.

> Student.attend_lecture(anita, “OOP”)

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Mini Quiz!

Q: Which of these are valid method calls?

> anita.attend_lecture(“OOP”)

> anita.attend_lecture(anita, “OOP”)

attend_lecture takes 2 arguments, but this call passes in 3 arguments! What are the 3 arguments?

> Student.attend_lecture(“OOP”)

No specific instance for this method was given.

> Student.attend_lecture(anita, “OOP”)

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Inheritance

Let’s reuse even more code!

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Current Implementation

class Dog(object):

def __init__(self, name, owner):

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Woof!”)

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Current Implementation

class Dog(object):

def __init__(self, name, owner):

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Woof!”)

class Cat(object):

def __init__(self, name, owner, lives=9):

self.name = name

self.owner = owner

self.lives = lives

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Meow!”)

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Current Implementation

class Dog(object):

def __init__(self, name, owner):

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Woof!”)

class Cat(object):

def __init__(self, name, owner, lives=9):

self.name = name

self.owner = owner

self.lives = lives

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Meow!”)

Any problems with this?

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Current Implementation

class Dog(object):

def __init__(self, name, owner):

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Woof!”)

class Cat(object):

def __init__(self, name, owner, lives=9):

self.name = name

self.owner = owner

self.lives = lives

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Meow!”)

So much repeated code! :(

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Current Implementation

class Dog(object):

def __init__(self, name, owner):

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Woof!”)

class Cat(object):

def __init__(self, name, owner, lives=9):

self.name = name

self.owner = owner

self.lives = lives

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name + “ says Meow!”)

So much repeated code! :(

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Let’s use inheritance!

Consolidate the similar code into one parent class that generalizes both subclasses!

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Let’s use inheritance!

class Pet(object):

def __init__(self, name, owner):

self.is_alive = True

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name)

Consolidate the similar code into one parent class that generalizes both subclasses!

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Let’s use inheritance!

class Pet(object):

def __init__(self, name, owner):

self.is_alive = True

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name)

Now we can have the Dog class extend the Pet class to inherit all of the instance variables and methods!

Syntax to do so:

class subclass(superclass)

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Let’s use inheritance!

class Pet(object):

def __init__(self, name, owner):

self.is_alive = True

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name)

class Dog(Pet):

Now we can have the Dog class extend the Pet class to inherit all of the instance variables and methods!

Syntax to do so:

class subclass(superclass)

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Let’s use inheritance!

class Pet(object):

def __init__(self, name, owner):

self.is_alive = True

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name)

class Dog(Pet):

If want a subclass to behave differently than parent class, override the method with a more specific implementation!

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Let’s use inheritance!

class Pet(object):

def __init__(self, name, owner):

self.is_alive = True

self.name = name

self.owner = owner

def eat(self, thing):

print(self.name + “ate a ” + str(thing) + “!”)

def talk(self):

print(self.name)

class Dog(Pet):

def talk(self):

print(self.name + “ says Woof!”)

If want a subclass to behave differently than parent class, override the method with a more specific implementation!

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Inheritance Hierarchy

Animal

Dog

Cat

Poodle

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Inheritance Hierarchy

Animal

Dog

Cat

Poodle

class Poodle(Dog)

MUST follow an IS-A relationship

a Poodle is a Dog