index.rst

title:	Magic methods for Muggles
data-transition-duration:	1
css:	psm.css

---

Magic methods for Muggles

Alex Hermida

@alexhermida

http://www.initios.com

---

id:	muggle

Muggle

"A person who is born to two non-magical parents and is incapable of performing magic"

---

---

Also known as..

Special

Dunder

Double-underscore

---

DISCLAIMER

Only.. Python 3

From scratch

---

Tipical method

def __init__(self):

---

def __whatever__(self):

---

id:	some-special-methods-1

Some Special methods 1/2

• string/bytes representation: __repr__, __str__, __format__, __bytes__
• conversion to number: __abs__, __bool__, __complex__, __int__, __float__, __hash__
• emulating collections: __len__, __getitem__, __setitem__, __delitem__, __contains__
• iteration: __iter__, __reversed__, __next__
• emulating callables: __call__
• context management: __enter__, __exit__

---

id:	some-special-methods-2

Some Special methods 2/2

• instance creation and destruction: __new__, __init__, __del__
• attribute management: __getattr__, __getattribute__, __setattr__, __delattr__, __dir__
• attribute descriptors: __get__, __set__, __delete__
• class services: __prepare__, __instancecheck__, __subclasscheck__
• operators: __add__ +, __sub__ -, __mul__ *, __lt__ >, __le__ <=, __eq__ ==

---

id:	objects-initialization-1

Objects Initialization

        def __init__(self, magic_types, strenth):
                self.magic_types = magic_types
                self.strenth = strenth

>>> wizard = Wizard('transfiguration', 8)
>>> wizard.magic_types
'transfiguration'

---

id:	objects-initialization-2

Objects Initialization

def __new__(cls[, ...]):

def __del__(self):

---

Representing objects

def __str__(self):

def __repr__(self):

Note

EXAMPLE 1

---

Containers

• List and dictionary-style access and modification.
• Membership testing
• Length checking
• Basic looping (implicit iterator)
• Reversal

---

Containers

__getitem__(self, index)

__setitem__(self, index, value)

__delitem__(self, index)

__len__(self)

__contains__(self, value)

__reversed__(self)

---

Containers

hermione = Wizard('tiger', False)

magicians = [harry, hermione]

main_character = magicians[0]
main_character = magicians.__getitem__(0)

magicians[1] = ron
magicians.__setitem__(1, ron)

del magicians[1]
magicians.__delitem__(1)

len(magicians)
magicians.__len__()

hermione in magicians
magicians.__contains__(hermione)

---

Attribute Access

__getattr__(self, name)

__setattr__(self, name, value)

__delattr__(self, name)

__getattribute__(self, name)

__dir__(self)

---

Attribute Access

def __getattr__(self, name):

Note

Example 2

---

Attribute Access

def __getattribute__(self, name):

---

id:	attribute-access

Attribute Access

class Muggle:
        def __getattr__(self, name):
                return 'I don´t have attr %s!' % name

        def __getattribute__(self, name):
                print('My attr: ', name)
                return self.tech

Note

Example-3

---

Magic example

class PoweredWizard:

Note

Example-4

---

Getting info about methods

object.__dir__(self)

Note

Example-5

---

Getting info about methods

• Attribute management
• Proxy methods
• Operators overloading
• Others..

---

The Zen of Python

• Explicit is better than implicit.
• In the face of ambiguity, refuse the temptation to guess.

---

id:	resources-links

Resources:

• https://docs.python.org/3/reference/datamodel.html#special-method-names
• http://www.rafekettler.com/magicmethods.html
• http://www.diveintopython3.net/special-method-names.html
• https://bitbucket.org/cliff/special_methods/
• http://harrypotter.wikia.com/

---

Thanks!

@alexhermida