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Dive into Object-oriented Python Leonardo Giordani lgiordani.com DjangoCon Europe 2015 – Cardiff, Wales

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https://github.com/lgiordani/oopy IPython Notebooks DjangoCon_Europe_2015/notebooks Python 3 code DjangoCon_Europe_2015/code/python3 Python 2 code DjangoCon_Europe_2015/notebooks

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I'm a software engineer, interested in operating systems, versioning, Python and software architecture. Coder since around 1988, Linux user since 1998, Python lover since 1999. Currently working with Python and C in the field of satellite remote sensing. about me The Digital Cat lgiordani.com https://twitter.com/ tw_lgiordani https://github.com/ lgiordani https://plus.google.com/u/ LeonardoGiordani

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import levels from djce2015 import oop_workshop def can_understand(user): return user.level >= levels.BEGINNER for you in oop_workshop.attendees: assert can_understand(you) about_you.py

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ABOUT THIS TUTORIAL 3 Objects and types Classes and members Delegation Polymorphism

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PART 1 Objects and types

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 data = (13, 63, 5, 378, 58, 40) def avg(d): return sum(d)/len(d) >>> avg(data) 92.83333333333333 Plain old procedures

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 door1 = [1, 'closed'] door2 = [2, 'closed'] def open_door(door): door[1] = 'open' >>> open_door(door1) >>> door1 [1, 'open'] Procedures can modify data

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 door1 = [1, 'closed'] door2 = [2, 'closed'] ldoor1 = [1, 'closed', 'unlocked'] def open_door(door): door[1] = 'open' def open_ldoor(door): if door[2] == 'unlocked': door[1] = 'open' Things can get complicated

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 door1 = [1, 'closed'] door2 = [2, 'closed'] ldoor1 = [1, 'closed', 'unlocked'] def open_door(door): door[1] = 'open' def open_ldoor(door): if door[2] == 'unlocked': door[1] = 'open' >>> open_door(door1) >>> door1 [1, 'open'] >>> open_ldoor(ldoor1) >>> ldoor1 [1, 'open', 'unlocked'] Things can get complicated

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Behavioural meaning The meaning of the word 'type'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Structural meaning The meaning of the word 'type'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The behavioural meaning is important

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The meaning of the word 'class'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The meaning of the word 'instance'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> a = 6 >>> a 6 >>> type(a) >>> a = int(6) >>> a 6 >>> a.__class__ You already used classes

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Python 2.x Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 You already used classes >>> a = 6 >>> a 6 >>> type(a) >>> a = int(6) >>> a 6 >>> a.__class__

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Find some types that Python provides out of the box. 2. Can you create a float variable without using the '.' character? 3. What is the difference between {1,2,3} and {'a':1, 'b':2}?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Find some types that Python provides out of the box. >>> type(4) >>> type(4.5) >>> type('some words') >>> type([1,2,3,4]) >>> type((1,2,3,4)) >>> type({1,2,3,4}) >>> type({'first name':'Ray', 'last name':'Stantz'}) >>> type(True)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Can you create a float variable without using the '.' character? >>> a = float(4) >>> type(a)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 3. What is the difference between {1,2,3} and {'a':1, 'b':2}? >>> type({1,2,3}) >>> type({'a':1, 'b':2})

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) Keep data and functions together

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) >>> door1.number 1 >>> door1.status 'closed' Keep data and functions together

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) >>> door1.number 1 >>> door1.status 'closed' >>> door1.open() Keep data and functions together

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) >>> door1.number 1 >>> door1.status 'closed' >>> door1.open() >>> door1.number 1 >>> door1.status 'open' Keep data and functions together

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Python 2.x Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The first class class Door(object): def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) >>> door1.number 1 >>> door1.status 'closed' The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) >>> door1.number 1 >>> door1.status 'closed' >>> door1.open() The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> type(door1) >>> door1.number 1 >>> door1.status 'closed' >>> door1.open() >>> door1.number 1 >>> door1.status 'open' The first class class Door: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Create a ColouredDoor class that has the 'colour' attribute. 2. Create a ClosedDoor class that has a default status of 'closed'. 3. Create a ToggleDoor class that has a method toggle() that toggles the status of the door.

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Create a ColouredDoor class that has the 'colour' attribute. class ColouredDoor: def __init__(self, number, status, colour): self.number = number self.status = status self.colour = colour def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Create a ClosedDoor class that has a default status of 'closed'. class ClosedDoor: def __init__(self, number, status='closed'): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 3. Create a ToggleDoor class that has a method toggle() that toggles the status of the door. class ToggleDoor: def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed' def toggle(self): d = {'open': 'closed', 'closed': 'open'} self.status = d[self.status]

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PART 2 Classes and members

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Where is the class of an object? >>> door1 = Door(1, 'closed') >>> door2 = Door(1, 'closed')

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Where is the class of an object? >>> door1 = Door(1, 'closed') >>> door2 = Door(1, 'closed') >>> hex(id(door1)) '0xb67e148c' >>> hex(id(door2)) '0xb67e144c'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Where is the class of an object? >>> door1 = Door(1, 'closed') >>> door2 = Door(1, 'closed') >>> hex(id(door1)) '0xb67e148c' >>> hex(id(door2)) '0xb67e144c' >>> hex(id(door1.__class__)) '0xb685f56c' >>> hex(id(door2.__class__)) '0xb685f56c'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Class attributes class Door: colour = 'brown' def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> door2 = Door(2, 'closed') Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> door2 = Door(2, 'closed') >>> Door.colour 'brown' >>> door1.colour 'brown' >>> door2.colour 'brown' Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.colour = 'white' Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.colour = 'white' >>> Door.colour 'white' >>> door1.colour 'white' >>> door2.colour 'white' Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.colour = 'white' >>> Door.colour 'white' >>> door1.colour 'white' >>> door2.colour 'white' >>> hex(id(Door.colour)) '0xb67e1500' >>> hex(id(door1.colour)) '0xb67e1500' >>> hex(id(door2.colour)) '0xb67e1500' Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} >>> door1.__dict__['colour'] Traceback (most recent call last): File "", line 1, in KeyError: 'colour' Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} >>> door1.__dict__['colour'] Traceback (most recent call last): File "", line 1, in KeyError: 'colour' >>> door1.__class__.__dict__['colour'] 'white' >>> door1.colour is Door.colour True Class attributes

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Door door1 door2 __getattribute__() __getattribute__() Let's dive into attribute resolution door1.colour Door.colour

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Let's dive into attribute resolution >>> door1 = Door(1, 'closed') >>> door1.colour = 'white' >>> door1.__dict__['colour'] 'white' >>> door1.__class__.__dict__['colour'] 'brown'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Let's dive into attribute resolution >>> door1 = Door(1, 'closed') >>> door1.colour = 'white' >>> door1.__dict__['colour'] 'white' >>> door1.__class__.__dict__['colour'] 'brown' >>> door1.colour 'white' >>> Door.colour 'brown'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Let's dive into attribute resolution >>> door1 = Door(1, 'closed') >>> door1.colour = 'white' >>> door1.__dict__['colour'] 'white' >>> door1.__class__.__dict__['colour'] 'brown' >>> door1.colour 'white' >>> Door.colour 'brown' >>> Door.colour = 'red'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Let's dive into attribute resolution >>> door1 = Door(1, 'closed') >>> door1.colour = 'white' >>> door1.__dict__['colour'] 'white' >>> door1.__class__.__dict__['colour'] 'brown' >>> door1.colour 'white' >>> Door.colour 'brown' >>> Door.colour = 'red' >>> door1.__dict__['colour'] 'white' >>> door1.__class__.__dict__['colour'] 'red'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the Door class adding a class attribute 'status' with value 'undefined'. Does it work? What happens to instances? 2. Modify the Door class adding a class attribute 'status' with value 'closed' and remove status from __init__(). Does it work? 3. Add a toggle() method to the previous class. What happens if you call toggle() on a fresh instance? Why?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the Door class adding a class attribute 'status' with value 'undefined'. Does it work? What happens to instances? class Door: colour = 'brown' status = 'undefined' def __init__(self, number, status): self.number = number self.status = status def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Modify the Door class adding a class attribute 'status' with value 'closed' and remove status from __init__(). Does it work? class Door: colour = 'brown' status = 'closed' def __init__(self, number): self.number = number def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 3. Add a toggle() method to the previous class. What happens if you call toggle() on a fresh instance? Why? class Door: colour = 'brown' status = 'closed' def __init__(self, number): self.number = number def toggle(self): d = {'open': 'closed', 'closed': 'open'} self.status = d[self.status]

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} >>> door1.colour is Door.colour True What about methods?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} >>> door1.colour is Door.colour True >>> door1.open is Door.open False What about methods?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} >>> door1.colour is Door.colour True >>> door1.open is Door.open False >>> Door.__dict__['open'] >>> Door.open What about methods?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} >>> door1.colour is Door.colour True >>> door1.open is Door.open False >>> Door.__dict__['open'] >>> Door.open >>> door1.open > What about methods?

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Python 2.x Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.__dict__ mappingproxy({'open': , 'colour': 'white', '__dict__': , '__weakref__': , '__init__': , '__module__': '__main__', '__doc__': None, 'close': }) >>> door1.__dict__ {'number': 1, 'status': 'closed'} >>> door1.colour is Door.colour True >>> door1.open is Door.open False >>> Door.__dict__['open'] >>> Door.open >>> door1.open > What about methods?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: open() missing 1 required positional argument: 'self' From functions to bound methods

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Python 2.x Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: unbound method open() must be called with Door instance as first argument (got nothing instead) From functions to bound methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: open() missing 1 required positional argument: 'self' >>> Door.open(door1) >>> door1.status 'open' From functions to bound methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: open() missing 1 required positional argument: 'self' >>> Door.open(door1) >>> door1.status 'open' >>> door1.__class__.__dict__['open'] From functions to bound methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: open() missing 1 required positional argument: 'self' >>> Door.open(door1) >>> door1.status 'open' >>> door1.__class__.__dict__['open'] >>> dir(door1.__class__.__dict__['open']) ['__annotations__', '__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__globals__', '__gt__', '__hash__', '__init__', '__kwdefaults__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__'] From functions to bound methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: open() missing 1 required positional argument: 'self' >>> Door.open(door1) >>> door1.status 'open' >>> door1.__class__.__dict__['open'] >>> dir(door1.__class__.__dict__['open']) ['__annotations__', '__call__', '__class__', '__closure__', ...,'__get__',...] >>> door1.__class__.__dict__['open'].__get__ From functions to bound methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: open() missing 1 required positional argument: 'self' >>> Door.open(door1) >>> door1.status 'open' >>> door1.__class__.__dict__['open'] >>> dir(door1.__class__.__dict__['open']) ['__annotations__', '__call__', '__class__', '__closure__', ...,'__get__',...] >>> door1.__class__.__dict__['open'].__get__ >>> door1.__class__.__dict__['open'].__get__(door1) > From functions to bound methods

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Python 2.x Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> Door.open() Traceback (most recent call last): File "", line 1, in TypeError: open() missing 1 required positional argument: 'self' >>> Door.open(door1) >>> door1.status 'open' >>> door1.__class__.__dict__['open'] >>> dir(door1.__class__.__dict__['open']) ['__annotations__', '__call__', '__class__', '__closure__', ...,'__get__',...] >>> door1.__class__.__dict__['open'].__get__ >>> door1.__class__.__dict__['open'].__get__(door1) > >>> door1.__class__.__dict__['open'].__get__(door1, Door) > From functions to bound methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class Door: colour = 'brown' def __init__(self, number, status): self.number = number self.status = status @classmethod def knock(cls): print("Knock!") def open(self): self.status = 'open' def close(self): self.status = 'closed' Class methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door1 = Door(1, 'closed') >>> door1.knock() Knock! >>> Door.knock() Knock! From functions to bound methods

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the Door class adding a class method 'paint' that accepts a 'colour' argument and changes the class attribute 'colour'. 2. Modify the Door class adding both a class method 'paint' and a standard method 'paint'. What happens?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the Door class adding a class method 'paint' that accepts a 'colour' argument and changes the class attribute 'colour'. class Door: colour = 'brown' def __init__(self, number, status): self.number = number self.status = status @classmethod def paint(cls, colour): cls.colour = colour def open(self): self.status = 'open' def close(self): self.status = 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Modify the Door class adding both a class method 'paint' and a standard method 'paint'. What happens? class Door: colour = 'brown' def __init__(self, number, status): self.number = number self.status = status @classmethod def paint(cls, colour): cls.colour = colour def paint(self, colour): self.colour = colour [...]

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PART 3 Delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Specialization Cat Animal

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Cat has all the features of Cat has all the features of Animal, i.e. 'moves' Animal, i.e. 'moves' Specialization Cat Animal

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Cat may provide new features, i.e. Cat may provide new features, i.e. 'has whiskers' 'has whiskers' Specialization Cat Animal

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Cat performs some or all the tasks performed Cat performs some or all the tasks performed by Animal in a different way, i.e. 'moves silently' by Animal in a different way, i.e. 'moves silently' Specialization Cat Animal

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Cat implements only 'new' or Cat implements only 'new' or 'changed' features 'changed' features Cat delegates the remaining Cat delegates the remaining features to Animal features to Animal Delegation Cat Animal

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Composition: 'has' Car Engine turn_on() Wheels steer() get_color()

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance: 'is' look() look() Cat Animal look() mew()

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance class SecurityDoor(Door): pass

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance class SecurityDoor(Door): pass >>> sdoor = SecurityDoor(1, 'closed')

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance class SecurityDoor(Door): pass >>> sdoor = SecurityDoor(1, 'closed') >>> SecurityDoor.colour is Door.colour True >>> sdoor.colour is Door.colour True

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance class SecurityDoor(Door): pass >>> sdoor = SecurityDoor(1, 'closed') >>> SecurityDoor.colour is Door.colour True >>> sdoor.colour is Door.colour True sdoor.colour sdoor.colour SecurityDoor.colour SecurityDoor.colour Door.colour Door.colour

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance >>> sdoor.__dict__ {'number': 1, 'status': 'closed'}

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance >>> sdoor.__dict__ {'number': 1, 'status': 'closed'} >>> sdoor.__class__.__dict__ mappingproxy({'__doc__': None, '__module__': '__main__'}) >>> Door.__dict__ mappingproxy({'__dict__': , 'colour': 'yellow', 'open': , '__init__': , '__doc__': None, 'close': , 'knock': , '__weakref__': , '__module__': '__main__', 'paint': })

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance >>> sdoor.__dict__ {'number': 1, 'status': 'closed'} >>> sdoor.__class__.__dict__ mappingproxy({'__doc__': None, '__module__': '__main__'}) >>> Door.__dict__ mappingproxy({'__dict__': , 'colour': 'yellow', 'open': , '__init__': , '__doc__': None, 'close': , 'knock': , '__weakref__': , '__module__': '__main__', 'paint': }) >>> SecurityDoor.__bases__ (,)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Inheritance >>> sdoor.__dict__ {'number': 1, 'status': 'closed'} >>> sdoor.__class__.__dict__ mappingproxy({'__doc__': None, '__module__': '__main__'}) >>> Door.__dict__ mappingproxy({'__dict__': , 'colour': 'yellow', 'open': , '__init__': , '__doc__': None, 'close': , 'knock': , '__weakref__': , '__module__': '__main__', 'paint': }) >>> SecurityDoor.__bases__ (,) >>> sdoor.knock > >>> sdoor.__class__.__bases__[0].__dict__['knock'].__get__(sdoor) >

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Overriding class SecurityDoor(Door): colour = 'grey' locked = True def open(self): if not self.locked: self.status = 'open'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Overriding class SecurityDoor(Door): colour = 'grey' locked = True def open(self): if not self.locked: self.status = 'open' >>> SecurityDoor.__dict__ mappingproxy({'__doc__': None, '__module__': '__main__', 'open': , 'colour': 'grey', 'locked': True})

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the SecurityDoor class adding a custom close_and_lock() method that changes status to 'closed' and locked to True. Test it. 2. Modify the SecurityDoor class adding a custom close() method that accepts a locked flag (with default). 3. Modify the SecurityDoor class adding a custom __init__() method that sets self.locked.

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the SecurityDoor class adding a custom close_and_lock() method that changes status to 'closed' and locked to True. Test it. class SecurityDoor(Door): colour = 'grey' locked = False def open(self): if not self.locked: self.status = 'open' def close_and_lock(self): self.status = 'closed' self.locked = True

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Modify the SecurityDoor class adding a custom close() method that accepts a locked flag (with default). class SecurityDoor(Door): colour = 'grey' locked = False def open(self): if not self.locked: self.status = 'open' def close(self, locked=False): self.status = 'closed' self.locked = locked

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 3. Modify the SecurityDoor class adding a custom __init__() method that sets self.locked. class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=False): self.number = number self.status = status self.locked = locked def open(self): if not self.locked: self.status = 'open'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Overriding class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=True): Door.__init__(self, number, status) self.locked = locked def open(self): if self.locked: return Door.open(self)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Overriding class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=True): Door.__init__(self, number, status) self.locked = locked def open(self): if self.locked: return Door.open(self) >>> sdoor = SecurityDoor(1, 'closed')

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Overriding class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=True): Door.__init__(self, number, status) self.locked = locked def open(self): if self.locked: return Door.open(self) >>> sdoor = SecurityDoor(1, 'closed') >>> sdoor.open() >>> sdoor.status 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Overriding class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=True): Door.__init__(self, number, status) self.locked = locked def open(self): if self.locked: return Door.open(self) >>> sdoor = SecurityDoor(1, 'closed') >>> sdoor.open() >>> sdoor.status 'closed' >>> sdoor.locked = False >>> sdoor.open() >>> sdoor.status 'open'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Avoid strong coupling class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=True): super().__init__(number, status) self.locked = locked def open(self): if self.locked: return super().open()

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Python 2.x Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Avoid strong coupling class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=True): super(SecurityDoor, self).__init__(number, status) self.locked = locked def open(self): if self.locked: return super(SecurityDoor, self).open()

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class SecurityDoor: colour = 'grey' def __init__(self, number, status, locked=True): self.door = Door(number, status) self.locked = locked def open(self): if self.locked: return self.door.open() def close(self): self.door.close() Composition

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class SecurityDoor: colour = 'grey' def __init__(self, number, status, locked=True): self.door = Door(number, status) self.locked = locked def open(self): if self.locked: return self.door.open() def close(self): self.door.close() >>> sdoor = SecurityDoor(1, 'closed') >>> sdoor.status Traceback (most recent call last): File "", line 1, in AttributeError: 'SecurityDorr' object has no attribute 'status' Composition

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class SecurityDoor: colour = 'grey' def __init__(self, number, status, locked=True): self.door = Door(number, status) self.locked = locked def open(self): if self.locked: return self.door.open() def close(self): self.door.close() def get_status(self): return self.door.status status = property(get_status) >>> sdoor = SecurityDoor(1, 'closed') >>> sdoor.status 'closed' Composition

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Python magic to the rescue class SecurityDoor: colour = 'grey' def __init__(self, number, status, locked=True): self.door = Door(number, status) self.locked = locked def open(self): if self.locked: return self.door.open() def close(self): self.door.close() def __getattr__(self, attr): return getattr(self.door, attr) >>> sdoor = SecurityDoor(1, 'closed') >>> sdoor.status 'closed'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Python magic to the rescue class SecurityDoor: colour = 'grey' def __init__(self, number, status, locked=True): self.door = Door(number, status) self.locked = locked def open(self): if self.locked: return self.door.open() #def close(self): # self.door.close() def __getattr__(self, attr): return getattr(self.door, attr)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class ComposedDoor: def __init__(self, number, status): self.door = Door(number, status) def __getattr__(self, attr): return getattr(self.door, attr) Composed inheritance?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the SecurityDoor class adding a custom close_and_lock() method. Use super(). Try and implement it with composition. 2. Modify the SecurityDoor class adding a custom close() method that accepts a locked flag (with default). Use super(). Try and implement it with composition.

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the SecurityDoor class adding a custom close_and_lock() method. Use super(). Try and implement it with composition. class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=False): super().__init__(number, status) self.locked = locked def open(self): if self.locked: return super().open() def close_and_lock(self): super().close() self.locked = True

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the SecurityDoor class adding a custom close_and_lock() method. Use super(). Try and implement it with composition. class SecurityDoor: colour = 'grey' def __init__(self, number, status, locked=False): self.door = Door(number, status) self.locked = locked def open(self): if self.locked: return self.door.open() def __getattr__(self, attr): return getattr(self.door, attr) def close_and_lock(self): self.door.close() self.locked = True

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Modify the SecurityDoor class adding a custom close() method that accepts a locked flag (with default). Use super(). Try and implement it with composition. class SecurityDoor(Door): colour = 'grey' def __init__(self, number, status, locked=False): super().__init__(number, status) self.locked = locked def open(self): if self.locked: return super().open() def close(self, locked=False): super().close() self.locked = locked

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Modify the SecurityDoor class adding a custom close() method that accepts a locked flag (with default). Use super(). Try and implement it with composition. class SecurityDoor: colour = 'grey' def __init__(self, number, status, locked=False): self.door = Door(number, status) self.locked = locked def open(self): if self.locked: return self.door.open() def __getattr__(self, attr): return getattr(self.door, attr) def close(self, locked=False): self.door.close() self.locked = locked

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 getattr() >>> l = [1,2,3] >>> dir(l) ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 getattr() >>> l = [1,2,3] >>> dir(l) ['__add__', '__class__', '__contains__', '__delattr__', ..., 'append', 'clear', 'copy', ...] >>> l.append

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 getattr() >>> l = [1,2,3] >>> dir(l) ['__add__', '__class__', '__contains__', '__delattr__', ..., 'append', 'clear', 'copy', ...] >>> l.append >>> a = l.append >>> a

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 getattr() >>> l = [1,2,3] >>> dir(l) ['__add__', '__class__', '__contains__', '__delattr__', ..., 'append', 'clear', 'copy', ...] >>> l.append >>> a = l.append >>> a >>> b = getattr(l, 'append') >>> b

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 getattr() >>> l = [1,2,3] >>> dir(l) ['__add__', '__class__', '__contains__', '__delattr__', ..., 'append', 'clear', 'copy', ...] >>> l.append >>> a = l.append >>> a >>> b = getattr(l, 'append') >>> b >>> a == b True >>> a is b False

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PART 4 Polymorphism

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 References >>> a = 5 >>> a 5

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 References >>> a = 5 >>> a 5 >>> type(a) >>> hex(id(a)) '0x83fe540'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 References >>> a = 5 >>> a 5 >>> type(a) >>> hex(id(a)) '0x83fe540' >>> a = 'five' >>> a 'five'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 References >>> a = 5 >>> a 5 >>> type(a) >>> hex(id(a)) '0x83fe540' >>> a = 'five' >>> a 'five' >>> type(a) >>> hex(id(a)) '0xb70d6560'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 References >>> a = 5 >>> a 5 >>> type(a) >>> hex(id(a)) '0x83fe540' >>> a = 'five' >>> a 'five' >>> type(a) >>> hex(id(a)) '0xb70d6560' Strong Strong type system: every type system: every variable has a type variable has a type

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 References >>> a = 5 >>> a 5 >>> type(a) >>> hex(id(a)) '0x83fe540' >>> a = 'five' >>> a 'five' >>> type(a) >>> hex(id(a)) '0xb70d6560' Dynamic Dynamic type system: the type type system: the type changes with the content changes with the content

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Every variable is a reference def echo(a): return a

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 Every variable is a reference def echo(a): return a >>> echo(5) 5 >>> echo('five') 'five'

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> 5 + 6 11 What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> 5 + 6 11 >>> 5.5 + 6.6 12.1 What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> 5 + 6 11 >>> 5.5 + 6.6 12.1 >>> "just a" + " string" 'just a string' What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> 5 + 6 11 >>> 5.5 + 6.6 12.1 >>> "just a" + " string" 'just a string' >>> [1,2,3] + [4,5,6] [1, 2, 3, 4, 5, 6] >>> (1,2,3) + (4,5,6) (1, 2, 3, 4, 5, 6) What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> 5 + 6 11 >>> 5.5 + 6.6 12.1 >>> "just a" + " string" 'just a string' >>> [1,2,3] + [4,5,6] [1, 2, 3, 4, 5, 6] >>> (1,2,3) + (4,5,6) (1, 2, 3, 4, 5, 6) >>> {'a':4, 'b':5} + {'c':7} Traceback (most recent call last): File "", line 1, in TypeError: unsupported operand type(s) for +: 'dict' and 'dict' What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> s = "Just a sentence" >>> len(s) 15 >>> l = [1, 2, 3] >>> len(l) 3 >>> d = {'a': 1, 'b': 2} >>> len(d) 2 What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> s = "Just a sentence" >>> len(s) 15 >>> l = [1, 2, 3] >>> len(l) 3 >>> d = {'a': 1, 'b': 2} >>> len(d) 2 >>> i = 5 >>> len(i) Traceback (most recent call last): File "", line 1, in TypeError: object of type 'int' has no len() What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> s.__len__() 15 >>> l.__len__() 3 >>> d.__len__() 2 What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> s.__len__() 15 >>> l.__len__() 3 >>> d.__len__() 2 >>> i.__len__() Traceback (most recent call last): File "", line 1, in AttributeError: 'int' object has no attribute '__len__' What is polymorphism?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> [1,2,3].__add__([4,5,6]) [1, 2, 3, 4, 5, 6] Polymorphism is based on delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> [1,2,3].__add__([4,5,6]) [1, 2, 3, 4, 5, 6] >>> dir([1,2,3]) ['__add__', '__class__', '__contains__', ...] Polymorphism is based on delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> [1,2,3].__add__([4,5,6]) [1, 2, 3, 4, 5, 6] >>> dir([1,2,3]) ['__add__', '__class__', '__contains__', ...] >>> 1 in [1,2,3] True >>> [1,2,3].__contains__(1) True Polymorphism is based on delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> [1,2,3].__add__([4,5,6]) [1, 2, 3, 4, 5, 6] >>> dir([1,2,3]) ['__add__', '__class__', '__contains__', ...] >>> 1 in [1,2,3] True >>> [1,2,3].__contains__(1) True >>> 6 in [1,2,3] False >>> [1,2,3].__contains__(6) False Polymorphism is based on delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 def sum(a, b): return a + b Polymorphism is based on delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 def sum(a, b): return a + b >>> sum(5,6) 11 >>> sum("Being ", "polymorphic") 'Being polymorphic' >>> sum([1,2,3], [4,5,6]) [1, 2, 3, 4, 5, 6] Polymorphism is based on delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 def sum(a, b): return a + b >>> sum(5,6) 11 >>> sum("Being ", "polymorphic") 'Being polymorphic' >>> sum([1,2,3], [4,5,6]) [1, 2, 3, 4, 5, 6] >>> sum([1,2,3], 8) Traceback (most recent call last): File "", line 1, in File "", line 2, in sum TypeError: can only concatenate list (not "int") to list Polymorphism is based on delegation

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Create a class that contains an integer as self.value and with a __len__ method that returns the number of digits of the integer. Does len() work for instances of this class? 2. Add a __contains__() method that returns True if self.value contains the given digit. Does 'in' work for this type? 3. Try str() on an instance of your class. What happens? How can you return a better string representation (e.g. to show the actual value)?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Create a class that contains an integer as self.value and with a __len__ method that returns the number of digits of the integer. Does len() work for instances of this class? class CustomInteger: def __init__(self, value): self.value = value def __len__(self): return len(str(self.value))

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Add a __contains__() method that returns True if self.value contains the given digit. Does 'in' work for this type? class CustomInteger: def __init__(self, value): self.value = value def __len__(self): return len(str(self.value)) def __contains__(self, digit): return str(digit) in str(self.value)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 3. Try str() on an instance of your class. What happens? How can you return a better string representation (e.g. to show the actual value)? class CustomInteger: def __init__(self, value): self.value = value def __len__(self): return len(str(self.value)) def __contains__(self, digit): return str(digit) in str(self.value) def __str__(self): return super().__str__() + ' [{}]'.format(self.value)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class Room: def __init__(self, door): self.door = door def open(self): self.door.open() def close(self): self.door.close() def is_open(self): return self.door.is_open() Polymorphism in action

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class Door: def __init__(self): self.status = "closed" def open(self): self.status = "open" def close(self): self.status = "closed" def is_open(self): return self.status == "open" Polymorphism in action

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 class BooleanDoor: def __init__(self): self.status = True def open(self): self.status = True def close(self): self.status = False def is_open(self): return self.status Polymorphism in action

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door = Door() >>> bool_door = BooleanDoor() Polymorphism in action

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door = Door() >>> bool_door = BooleanDoor() >>> room = Room(door) >>> bool_room = Room(bool_door) Polymorphism in action

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door = Door() >>> bool_door = BooleanDoor() >>> room = Room(door) >>> bool_room = Room(bool_door) >>> room.open() >>> room.is_open() True >>> room.close() >>> room.is_open() False Polymorphism in action

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 >>> door = Door() >>> bool_door = BooleanDoor() >>> room = Room(door) >>> bool_room = Room(bool_door) >>> room.open() >>> room.is_open() True >>> room.close() >>> room.is_open() False >>> bool_room.open() >>> bool_room.is_open() True >>> bool_room.close() >>> bool_room.is_open() False Polymorphism in action

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the Room, the Door and the BooleanDoor classes to add a toggle() method that changes open status to closed and vice versa. 2. Change the Room class such that it accepts a class instead of an instance. How do you manage it into __init__()? Does it still work? 3. Create a PetDoor object that inherits from Door (or BooleanDoor). Add the suitable methods to manage the small pet door. Does the Room work? 4. May you reuse the Door to create the pet door?

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 1. Modify the Room, the Door and the BooleanDoor classes to add a toggle() method that changes open status to closed and vice versa. class Room: def __init__(self, door): self.door = door def open(self): self.door.open() def close(self): self.door.close() def is_open(self): return self.door.is_open() def toggle(self): if self.door.is_open(): self.door.close() else: self.door.open()

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 2. Change the Room class such that it accepts a class instead of an instance. How do you manage it into __init__()? Does it still work? class Room: def __init__(self, door_cls): self.door = door_cls() def open(self): self.door.open() def close(self): self.door.close() def is_open(self): return self.door.is_open() >>> room = Room(Door) >>> bool_room = Room(BooleanDoor)

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 3. Create a PetDoor object that inherits from Door (or BooleanDoor). Add the suitable methods to manage the small pet door. Does the Room work? class PetDoor(BooleanDoor): def __init__(self): super().__init__() self.pet_door = "open" def open_pet_door(self): self.pet_door = "open" def close_pet_door(self): self.pet_door = "closed"

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 H om ew ork 4. May you reuse the Door to create the pet door? class PetDoor(BooleanDoor): def __init__(self): super().__init__() self.pet_door = BooleanDoor() def open_pet_door(self): self.pet_door.open() def close_pet_door(self): self.pet_door.close()

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 “Ask for permission” style if hasattr(someobj, 'open'): [...] else: [...] It It has has the attribute the attribute

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Dive into Object-oriented Python – lgiordani.com - CC BY-SA 4.0 “Ask for permission” style try: someobj.open() [...] except AttributeError: [...] It It behaves behaves like it has like it has the attribute the attribute

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A lot of people provided free information and code Font aswesome icons by Freepik Python 3 OOP series http://lgiordani.com/blog/categories/python3/ Some links about Python OOP http://goo.gl/UBdJDT CAST

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Dive into Object-oriented Python Leonardo Giordani lgiordani.com DjangoCon Europe 2015 – Cardiff, Wales