Inheritance Announcements Attributes Methods and Functions 4 - - PowerPoint PPT Presentation

Inheritance

Announcements

Attributes

Methods and Functions

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Methods and Functions

Python distinguishes between:

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Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and

4

Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked

4

Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method

4

Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit)

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Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit) <class 'function'>

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Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit) <class 'function'> >>> type(tom_account.deposit)

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Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit) <class 'function'> >>> type(tom_account.deposit) <class 'method'>

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Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit) <class 'function'> >>> type(tom_account.deposit) <class 'method'> >>> Account.deposit(tom_account, 1001) 1011

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Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit) <class 'function'> >>> type(tom_account.deposit) <class 'method'> >>> Account.deposit(tom_account, 1001) 1011 >>> tom_account.deposit(1004) 2015

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Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit) <class 'function'> >>> type(tom_account.deposit) <class 'method'> >>> Account.deposit(tom_account, 1001) 1011 >>> tom_account.deposit(1004) 2015

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Function: all arguments within parentheses

Methods and Functions

Python distinguishes between:

• Functions, which we have been creating since the beginning of the course, and
• Bound methods, which couple together a function and the object on which that

method will be invoked Object + Function = Bound Method >>> type(Account.deposit) <class 'function'> >>> type(tom_account.deposit) <class 'method'> >>> Account.deposit(tom_account, 1001) 1011 >>> tom_account.deposit(1004) 2015

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Function: all arguments within parentheses Method: One object before the dot and

• ther arguments within parentheses

Terminology: Attributes, Functions, and Methods

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Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs

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Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes

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Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance

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Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance

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Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance Terminology:

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Class
 Attributes


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance Terminology:

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Class
 Attributes
 Functions


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance Terminology:

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Class
 Attributes
 Functions


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance

Methods

Terminology:

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Class
 Attributes
 Functions


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance

Methods

Terminology: Python object system:

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Class
 Attributes
 Functions


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance

Methods

Functions are objects Terminology: Python object system:

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Class
 Attributes
 Functions


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance

Methods

Functions are objects Bound methods are also objects: a function that has its first parameter "self" already bound to an instance Terminology: Python object system:

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Class
 Attributes
 Functions


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance

Methods

Functions are objects Bound methods are also objects: a function that has its first parameter "self" already bound to an instance Dot expressions evaluate to bound methods for class attributes that are functions Terminology: Python object system:

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Class
 Attributes
 Functions


Terminology: Attributes, Functions, and Methods

All objects have attributes, which are name-value pairs Classes are objects too, so they have attributes Instance attribute: attribute of an instance Class attribute: attribute of the class of an instance

Methods

Functions are objects Bound methods are also objects: a function that has its first parameter "self" already bound to an instance Dot expressions evaluate to bound methods for class attributes that are functions Terminology: Python object system:

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<instance>.<method_name>

Looking Up Attributes by Name

<expression> . <name>

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Looking Up Attributes by Name

<expression> . <name> To evaluate a dot expression:

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Looking Up Attributes by Name

<expression> . <name> To evaluate a dot expression: 1. Evaluate the <expression> to the left of the dot, which yields the object of the dot expression

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Looking Up Attributes by Name

<expression> . <name> To evaluate a dot expression: 1. Evaluate the <expression> to the left of the dot, which yields the object of the dot expression 2. <name> is matched against the instance attributes of that object; if an attribute with that name exists, its value is returned

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Looking Up Attributes by Name

<expression> . <name> To evaluate a dot expression: 1. Evaluate the <expression> to the left of the dot, which yields the object of the dot expression 2. <name> is matched against the instance attributes of that object; if an attribute with that name exists, its value is returned 3. If not, <name> is looked up in the class, which yields a class attribute value

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Looking Up Attributes by Name

<expression> . <name> To evaluate a dot expression: 1. Evaluate the <expression> to the left of the dot, which yields the object of the dot expression 2. <name> is matched against the instance attributes of that object; if an attribute with that name exists, its value is returned 3. If not, <name> is looked up in the class, which yields a class attribute value 4. That value is returned unless it is a function, in which case a bound method is returned instead

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Class Attributes

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Class Attributes

Class attributes are "shared" across all instances of a class because they are attributes

• f the class, not the instance

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Class Attributes

Class attributes are "shared" across all instances of a class because they are attributes

• f the class, not the instance

class Account: interest = 0.02 # A class attribute def __init__(self, account_holder): self.balance = 0 self.holder = account_holder # Additional methods would be defined here

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Class Attributes

Class attributes are "shared" across all instances of a class because they are attributes

• f the class, not the instance

class Account: interest = 0.02 # A class attribute def __init__(self, account_holder): self.balance = 0 self.holder = account_holder # Additional methods would be defined here

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>>> tom_account = Account('Tom')

Class Attributes

Class attributes are "shared" across all instances of a class because they are attributes

• f the class, not the instance

class Account: interest = 0.02 # A class attribute def __init__(self, account_holder): self.balance = 0 self.holder = account_holder # Additional methods would be defined here

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>>> tom_account = Account('Tom') >>> jim_account = Account('Jim')

Class Attributes

Class attributes are "shared" across all instances of a class because they are attributes

• f the class, not the instance

class Account: interest = 0.02 # A class attribute def __init__(self, account_holder): self.balance = 0 self.holder = account_holder # Additional methods would be defined here

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>>> tom_account = Account('Tom') >>> jim_account = Account('Jim') >>> tom_account.interest 0.02

Class Attributes

Class attributes are "shared" across all instances of a class because they are attributes

• f the class, not the instance

class Account: interest = 0.02 # A class attribute def __init__(self, account_holder): self.balance = 0 self.holder = account_holder # Additional methods would be defined here The interest attribute is not part of the instance; it's part of the class!

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>>> tom_account = Account('Tom') >>> jim_account = Account('Jim') >>> tom_account.interest 0.02

Class Attributes

Class attributes are "shared" across all instances of a class because they are attributes

• f the class, not the instance

class Account: interest = 0.02 # A class attribute def __init__(self, account_holder): self.balance = 0 self.holder = account_holder # Additional methods would be defined here The interest attribute is not part of the instance; it's part of the class!

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>>> tom_account = Account('Tom') >>> jim_account = Account('Jim') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02

Attribute Assignment

Assignment to Attributes

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Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

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Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute

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Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

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Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

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class Account: interest = 0.02 def __init__(self, holder): self.holder = holder self.balance = 0 ... tom_account = Account('Tom')

Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

tom_account.interest = 0.08

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class Account: interest = 0.02 def __init__(self, holder): self.holder = holder self.balance = 0 ... tom_account = Account('Tom')

Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

tom_account.interest = 0.08 This expression evaluates to an

• bject

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class Account: interest = 0.02 def __init__(self, holder): self.holder = holder self.balance = 0 ... tom_account = Account('Tom')

Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

tom_account.interest = 0.08 But the name (“interest”) is not looked up This expression evaluates to an

• bject

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class Account: interest = 0.02 def __init__(self, holder): self.holder = holder self.balance = 0 ... tom_account = Account('Tom')

Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

tom_account.interest = 0.08 But the name (“interest”) is not looked up Attribute assignment statement adds

• r modifies the

attribute named “interest” of tom_account This expression evaluates to an

• bject

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class Account: interest = 0.02 def __init__(self, holder): self.holder = holder self.balance = 0 ... tom_account = Account('Tom')

Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

tom_account.interest = 0.08 But the name (“interest”) is not looked up Attribute assignment statement adds

• r modifies the

attribute named “interest” of tom_account Instance Attribute Assignment : This expression evaluates to an

• bject

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class Account: interest = 0.02 def __init__(self, holder): self.holder = holder self.balance = 0 ... tom_account = Account('Tom')

Assignment to Attributes

Assignment statements with a dot expression on their left-hand side affect attributes for the object of that dot expression

• If the object is an instance, then assignment sets an instance attribute
• If the object is a class, then assignment sets a class attribute

tom_account.interest = 0.08 But the name (“interest”) is not looked up Attribute assignment statement adds

• r modifies the

attribute named “interest” of tom_account Instance Attribute Assignment : Account.interest = 0.04 Class Attribute Assignment : This expression evaluates to an

• bject

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class Account: interest = 0.02 def __init__(self, holder): self.holder = holder self.balance = 0 ... tom_account = Account('Tom')

Attribute Assignment Statements

interest: 0.02 (withdraw, deposit, __init__) Account class attributes

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Attribute Assignment Statements

>>> jim_account = Account('Jim') interest: 0.02 (withdraw, deposit, __init__) Account class attributes

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Attribute Assignment Statements

>>> jim_account = Account('Jim') interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' Account class attributes

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Instance attributes of jim_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' Account class attributes

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Instance attributes of jim_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04 interest: 0.08

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 >>> jim_account.interest 0.08 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04 interest: 0.08

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 >>> jim_account.interest 0.08 >>> tom_account.interest 0.04 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04 interest: 0.08

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 >>> jim_account.interest 0.08 >>> tom_account.interest 0.04 >>> Account.interest = 0.05 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04 interest: 0.08

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 >>> jim_account.interest 0.08 >>> tom_account.interest 0.04 >>> Account.interest = 0.05 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04 interest: 0.08 0.05

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 >>> jim_account.interest 0.08 >>> tom_account.interest 0.04 >>> Account.interest = 0.05 >>> tom_account.interest 0.05 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04 interest: 0.08 0.05

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Instance attributes of jim_account Instance attributes of tom_account

Attribute Assignment Statements

>>> jim_account = Account('Jim') >>> tom_account = Account('Tom') >>> tom_account.interest 0.02 >>> jim_account.interest 0.02 >>> Account.interest = 0.04 >>> tom_account.interest 0.04 >>> jim_account.interest 0.04 >>> jim_account.interest = 0.08 >>> jim_account.interest 0.08 >>> tom_account.interest 0.04 >>> Account.interest = 0.05 >>> tom_account.interest 0.05 >>> jim_account.interest 0.08 interest: 0.02 (withdraw, deposit, __init__) balance: 0 holder: 'Jim' balance: 0 holder: 'Tom' Account class attributes 0.04 interest: 0.08 0.05

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Instance attributes of jim_account Instance attributes of tom_account

Inheritance

Inheritance

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Inheritance

Inheritance is a technique for relating classes together

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Inheritance

Inheritance is a technique for relating classes together A common use: Two similar classes differ in their degree of specialization

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Inheritance

Inheritance is a technique for relating classes together A common use: Two similar classes differ in their degree of specialization The specialized class may have the same attributes as the general class, along with some special-case behavior

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Inheritance

Inheritance is a technique for relating classes together A common use: Two similar classes differ in their degree of specialization The specialized class may have the same attributes as the general class, along with some special-case behavior

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class <Name>(<Base Class>): <suite>

Inheritance

Inheritance is a technique for relating classes together A common use: Two similar classes differ in their degree of specialization The specialized class may have the same attributes as the general class, along with some special-case behavior

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class <Name>(<Base Class>): <suite> Conceptually, the new subclass inherits attributes of its base class

Inheritance

Inheritance is a technique for relating classes together A common use: Two similar classes differ in their degree of specialization The specialized class may have the same attributes as the general class, along with some special-case behavior

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class <Name>(<Base Class>): <suite> Conceptually, the new subclass inherits attributes of its base class The subclass may override certain inherited attributes

Inheritance

Inheritance is a technique for relating classes together A common use: Two similar classes differ in their degree of specialization The specialized class may have the same attributes as the general class, along with some special-case behavior

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class <Name>(<Base Class>): <suite> Conceptually, the new subclass inherits attributes of its base class The subclass may override certain inherited attributes Using inheritance, we implement a subclass by specifying its differences from the the base class

Inheritance Example

A CheckingAccount is a specialized type of Account

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom')

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account):

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals."""

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount):

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

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Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

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• r

return super().withdraw( amount + self.withdraw_fee)

Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

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• r

return super().withdraw( amount + self.withdraw_fee)

Inheritance Example

A CheckingAccount is a specialized type of Account >>> ch = CheckingAccount('Tom') >>> ch.interest # Lower interest rate for checking accounts 0.01 >>> ch.deposit(20) # Deposits are the same 20 >>> ch.withdraw(5) # Withdrawals incur a $1 fee 14 Most behavior is shared with the base class Account class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

13

Looking Up Attribute Names on Classes

Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class: Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class:

• 1. If it names an attribute in the class, return the attribute value.

Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class:

• 1. If it names an attribute in the class, return the attribute value.
• 2. Otherwise, look up the name in the base class, if there is one.

Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class:

• 1. If it names an attribute in the class, return the attribute value.
• 2. Otherwise, look up the name in the base class, if there is one.

>>> ch = CheckingAccount('Tom') # Calls Account.__init__ Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class:

• 1. If it names an attribute in the class, return the attribute value.
• 2. Otherwise, look up the name in the base class, if there is one.

>>> ch = CheckingAccount('Tom') # Calls Account.__init__ >>> ch.interest # Found in CheckingAccount 0.01 Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class:

• 1. If it names an attribute in the class, return the attribute value.
• 2. Otherwise, look up the name in the base class, if there is one.

>>> ch = CheckingAccount('Tom') # Calls Account.__init__ >>> ch.interest # Found in CheckingAccount 0.01 >>> ch.deposit(20) # Found in Account 20 Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class:

• 1. If it names an attribute in the class, return the attribute value.
• 2. Otherwise, look up the name in the base class, if there is one.

>>> ch = CheckingAccount('Tom') # Calls Account.__init__ >>> ch.interest # Found in CheckingAccount 0.01 >>> ch.deposit(20) # Found in Account 20 >>> ch.withdraw(5) # Found in CheckingAccount 14 Base class attributes aren't copied into subclasses!

14

Looking Up Attribute Names on Classes

To look up a name in a class:

• 1. If it names an attribute in the class, return the attribute value.
• 2. Otherwise, look up the name in the base class, if there is one.

>>> ch = CheckingAccount('Tom') # Calls Account.__init__ >>> ch.interest # Found in CheckingAccount 0.01 >>> ch.deposit(20) # Found in Account 20 >>> ch.withdraw(5) # Found in CheckingAccount 14 Base class attributes aren't copied into subclasses!

14

(Demo)

Object-Oriented Design

Designing for Inheritance

16

Designing for Inheritance

Don't repeat yourself; use existing implementations

16

Designing for Inheritance

Don't repeat yourself; use existing implementations

16

class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

Designing for Inheritance

Don't repeat yourself; use existing implementations Attributes that have been overridden are still accessible via class objects

16

class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

Designing for Inheritance

Don't repeat yourself; use existing implementations Attributes that have been overridden are still accessible via class objects Attribute look-up

• n base class

16

class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

Designing for Inheritance

Don't repeat yourself; use existing implementations Attributes that have been overridden are still accessible via class objects Look up attributes on instances whenever possible Attribute look-up

• n base class

16

class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

Designing for Inheritance

Don't repeat yourself; use existing implementations Attributes that have been overridden are still accessible via class objects Look up attributes on instances whenever possible Attribute look-up

• n base class

Preferred to CheckingAccount.withdraw_fee to allow for specialized accounts

16

class CheckingAccount(Account): """A bank account that charges for withdrawals.""" withdraw_fee = 1 interest = 0.01 def withdraw(self, amount): return Account.withdraw(self, amount + self.withdraw_fee)

Inheritance and Composition

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor Inheritance is best for representing is-a relationships

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor Inheritance is best for representing is-a relationships

• E.g., a checking account is a specific type of account

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor Inheritance is best for representing is-a relationships

• E.g., a checking account is a specific type of account
• So, CheckingAccount inherits from Account

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor Inheritance is best for representing is-a relationships

• E.g., a checking account is a specific type of account
• So, CheckingAccount inherits from Account

Composition is best for representing has-a relationships

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor Inheritance is best for representing is-a relationships

• E.g., a checking account is a specific type of account
• So, CheckingAccount inherits from Account

Composition is best for representing has-a relationships

• E.g., a bank has a collection of bank accounts it manages

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor Inheritance is best for representing is-a relationships

• E.g., a checking account is a specific type of account
• So, CheckingAccount inherits from Account

Composition is best for representing has-a relationships

• E.g., a bank has a collection of bank accounts it manages
• So, A bank has a list of accounts as an attribute

17

Inheritance and Composition

Object-oriented programming shines when we adopt the metaphor Inheritance is best for representing is-a relationships

• E.g., a checking account is a specific type of account
• So, CheckingAccount inherits from Account

Composition is best for representing has-a relationships

• E.g., a bank has a collection of bank accounts it manages
• So, A bank has a list of accounts as an attribute

17

(Demo)

Attributes Lookup Practice

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z z: -1 f: <class A> func f(self, x)

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z z: -1 f: <class A> func f(self, x) Global

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z z: -1 f: <class A> func f(self, x) Global A

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) Global A

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) Global A B

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) Global A B

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) Global A B C

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) Global A B C

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) Global A B C a

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: ... Global A B C a

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: ... Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: ... n: 5 Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C instance> z: 2 ... n: 5 Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C instance> z: 2 ... n: 5 4 Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C instance> z: 2 ... n: 5 4 True Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C instance> z: 2 n: 5 4 True Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <B inst> z: <C instance> z: 2 n: 5 4 True Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C inst> z: <B inst> z: <C instance> z: 2 n: 5 4 True Global A B C a b

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C inst> z: <B inst> z: <C instance> z: 2 n: 5 4 True Global A B C a b 1

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C inst> z: <B inst> z: <C instance> z: 2 n: 5 4 True False Global A B C a b 1

Inheritance and Attribute Lookup

class A: z = -1 def f(self, x): return B(x-1) class B(A): n = 4 def __init__(self, y): if y: self.z = self.f(y) else: self.z = C(y+1) class C(B): def f(self, x): return x a = A() b = B(1) b.n = 5

19

>>> a.z == C.z >>> C(2).n Which evaluates 
 to an integer? b.z b.z.z b.z.z.z b.z.z.z.z None of these >>> a.z == b.z <A instance> z: -1 f: <class A> func f(self, x) n: 4 __init__: <class B inherits from A> func __init__(self, y) f: <class C inherits from B> func f(self, x) <B instance> z: <C inst> z: <B inst> z: <C instance> z: 2 n: 5 4 True False Global A B C a b 1

Multiple Inheritance

Multiple Inheritance

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee)

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee) A class may inherit from multiple base classes in Python

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee) A class may inherit from multiple base classes in Python CleverBank marketing executive has an idea:

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee) A class may inherit from multiple base classes in Python CleverBank marketing executive has an idea:

• Low interest rate of 1%

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee) A class may inherit from multiple base classes in Python CleverBank marketing executive has an idea:

• Low interest rate of 1%
• A $1 fee for withdrawals

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee) A class may inherit from multiple base classes in Python CleverBank marketing executive has an idea:

• Low interest rate of 1%
• A $1 fee for withdrawals
• A $2 fee for deposits

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee) A class may inherit from multiple base classes in Python CleverBank marketing executive has an idea:

• Low interest rate of 1%
• A $1 fee for withdrawals
• A $2 fee for deposits
• A free dollar when you open your account

21

Multiple Inheritance

class SavingsAccount(Account): deposit_fee = 2 def deposit(self, amount): return Account.deposit(self, amount - self.deposit_fee) class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! A class may inherit from multiple base classes in Python CleverBank marketing executive has an idea:

• Low interest rate of 1%
• A $1 fee for withdrawals
• A $2 fee for deposits
• A free dollar when you open your account

21

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar!

22

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! >>> such_a_deal = AsSeenOnTVAccount('John')

22

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! >>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1

22

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! >>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1 Instance attribute

22

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! >>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1 >>> such_a_deal.deposit(20) 19 Instance attribute

22

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! >>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1 >>> such_a_deal.deposit(20) 19 Instance attribute SavingsAccount method

22

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! >>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1 >>> such_a_deal.deposit(20) 19 >>> such_a_deal.withdraw(5) 13 Instance attribute SavingsAccount method

22

Multiple Inheritance

A class may inherit from multiple base classes in Python. class AsSeenOnTVAccount(CheckingAccount, SavingsAccount): def __init__(self, account_holder): self.holder = account_holder self.balance = 1 # A free dollar! >>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1 >>> such_a_deal.deposit(20) 19 >>> such_a_deal.withdraw(5) 13 Instance attribute SavingsAccount method CheckingAccount method

22

Resolving Ambiguous Class Attribute Names

23

>>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1 >>> such_a_deal.deposit(20) 19 >>> such_a_deal.withdraw(5) 13 Instance attribute SavingsAccount method CheckingAccount method

Resolving Ambiguous Class Attribute Names

Account CheckingAccount SavingsAccount AsSeenOnTVAccount

23

>>> such_a_deal = AsSeenOnTVAccount('John') >>> such_a_deal.balance 1 >>> such_a_deal.deposit(20) 19 >>> such_a_deal.withdraw(5) 13 Instance attribute SavingsAccount method CheckingAccount method

Complicated Inheritance

Biological Inheritance

25

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Mom Dad

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Mom Dad You

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Mom Dad You

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Mom Dad You Half some_guy

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Mom Dad You Half some_guy Half Cousin some_other_guy

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Mom Dad You Half Half Cousin some_other_guy

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Double Mom Dad You Half Half Cousin some_other_guy

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Double Mom Dad You Half Half Cousin some_other_guy Double

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Double Mom Dad You Half Double Half Uncle Half Cousin some_other_guy Double

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Double Mom Dad You Half Double Half Uncle Half Cousin Double

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Double Quadruple Mom Dad You Half Double Half Uncle Half Cousin

Biological Inheritance

25

Grandma Grandpa Gramammy Grandaddy Aunt Double Quadruple Mom Dad You Half Double Half Uncle Half Cousin

Moral of the story: Inheritance can be complicated, so don't overuse it!