metaprogramação em python: decorators e metaclasses

metaprogramação em python:

metaclass e decorators

@felipevolponegithub.com/felipevolpone

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http://github.com/felipevolpone

http://facebook.com/felipevolpone

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por que

metaprogramação?

aprender

por que

é poderoso

reutilizar código

aumentar abstração

criar APIs mais ricas

decoratorshttps://www.python.org/dev/peps/pep-0318/

python 2.4

o que é!

!

@staticmethod def say_hello(): return "Hello TDC :)" !

#flask @app.route('/') def hello_rest(): return "Hello TDC :)"

como funciona

def log(func): def internal(): return func() return internal !

@log def say_hello(): return "Hello TDC"

!

def log(func): … !

#@log def say_hello(): return "Hello TDC" !

say_hello = log(say_hello)




}

print say_hello <function say_hello at 0x105909c80> !

say_hello = log(say_hello) print say_hello <function internal at 0x105909cf8>



say_hello = log(say_hello) print say_hello()


def say_hello(): return "Hello TDC" !

say_hello = log(say_hello) print say_hello() > "Hello TDC"

from datetime import datetime !def log(func): def internal(): now = datetime.now() \ .strftime(“%d/%m/%Y %H:%M:%S") print "Funcao chamada: %s as %s" % (func.func_name, now) return func() return internal !print say_hello() > "Funcao chamada: say_hello as 17/07/2015 16:45:36" > "Hello TDC"

def log(func): def internal(): now = … print "Funcao chamada ..." return func() return internal !@log def say_hello(message): return message @log def goodbye(): return “goodbye" !print goodbye() > Funcao chamada: goodbye as 17/07/2015 16:30:23 > goodbye print say_hello("#python no TDC") > TypeError: internal() takes no arguments (1 given)

!

def log(func): def internal(*args, **kwargs): now = … print "Funcao chamada: …" return func(*args, **kwargs) return internal

args é iterável kwargs é {}

def example(func): def internal(*args, **kwargs): return func(*args, **kwargs) return internal !

@example def sum_base(a, b, base=12): return a+b+base !

print sum_base(6, 10, base=12) > 28

combinando decorators

@timestamp @log def say_message(msg): return msg !

sum_func = timestamp(log(say_message))

[email protected]('/about') def about(): return 'The about page' [email protected]('Failing test') def test_example(self): self.assertEquals(1, 2) !

def authentication(msg): ! def decorator(func): def internal(*args, **kwargs): user = get_session_user() if user.valid: return func(*args, **kwargs) else: raise Exception(msg) return internal ! return decorator

@authentication("User is not valid") def say_hello(): return "Hello TDC" !say_hello = \ authentication(“User is not valid")(say_hello) !#quando usuario nao eh valido print say_hello() > raise Exception(msg) Exception: User is not valid

@json @flask.get('/products/') def get_products(): return {'products': get_products()} !@html def get_static_file(file_path): return open(file_path) !@auth('admin') def delete_user(): pass !@convert_object @flask.post('/user/<id>') def get_user(model_user) # transforma json em objeto python model_user.put()

cobre 90% dos casos

def example(func): def internal(*args, **kwargs): """Useless decorator""" return func(*args, **kwargs) return internal !@example def say_hello(): """A simple function that says hello TDC""" return "Hello TDC" !print say_hello.func_name print say_hello.func_doc > "internal" > "Useless decorator"

def example(func): def internal(*args, **kwargs): "Useless decorator" return func(*args, **kwargs) internal.func_name = func.func_name internal.func_doc = func.func_doc return internal !@example def say_hello(): "Function that says hello TDC" return "Hello TDC" !print say_hello.func_name, say_hello.func_doc > “say_hello" "Function that says hello TDC"

import wrapt

http://pyvideo.org/video/2617/advanced-methods-for-creat

metaclasses

class User(object): pass !a = User() type(a) > __main__.User !type(User) > type !type(str) > type

isinstance(User, type) > True !isinstance(str, type) > True

metaclass class

class

class

User object type

metaclass class

subclass instance

str instance type

user

object

instance

"tdc2015"instance

__init__

__new__

instância

user = User()metac

lass

clas

s

1

2

4

__call____init__

1.1 1.2

class MyMetaclass(type): pass !class Person(object): __metaclass__ = MyMetaclass !print type(Person) > <class '__main__. MyMetaclass'>

exemplos

class Person(object): __metaclass__ = LogMetaclass ! def say_hello(self): return 'hello tdc'

import inspect, wrap !def log_decorator(func): @wrapt def inner(*args, **kwargs): print '[Logging] %s was called' % (func.func_name,) return func(*args, **kwargs) return inner !class LogMetaclass(type): ! def __init__(cls, *args, **kwargs): for prop in args[2]: #propriedades de person method = getattr(cls, prop) ! if inspect.ismethod(method): decorated_method = log_decorator(method) setattr(cls, prop, decorated_method) ! return type.__init__(cls, *args, **kwargs)

class Person(object): __metaclass__ = LogMetaclass ! def say_hello(self): return 'hello tdc' !u = Person() print u.say_hello() > "[Logging] say_hello was called" > “hello tdc"

import inspect !!class ModelBasicProtocol(type): ! def __new__(cls, name, parents, dct): ! if '__init__' in dct: init_function = dct['__init__'] init_inspection = inspect.getargspec(init_function) ! if init_inspection.defaults is None and len(init_inspection.args) > 1: raise Exception(‘The object must have a keywords arguments in __init__') ! return type.__new__(cls, name, parents, dct)

class TableProduct(object): __metaclass__ = ModelBasicProtocol ! def __init__(self, name): pass !e = TableProduct('Notebook') > Exception: A modelobject must have a keywords arguments in __init__

descriptors

https://speakerdeck.com/ramalho/python-encapsulation-with-descriptors-1

from google.appengine.ext import ndb !class Event(ndb.Model): name = ndb.StringProperty(required=True) description = ndb.TextProperty(required=True) logo = ndb.BlobKeyProperty(default=None) date = ndb.DateTimeProperty()

@felipevolpone

metaprogramação em python: decorators e metaclasses

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