4.4. Decorator Function with Cls¶
4.4.1. Rationale¶
mydecoratoris a decorator nameMyClassis a class name
Syntax:
>>> @mydecorator
... class MyClass:
... ...
Is equivalent to:
>>> MyClass = mydecorator(MyClass)
4.4.2. Syntax¶
mydecoratoris a decorator nameMyClassis a class name
>>> def decorator(cls):
... class Wrapper(cls):
... def __new__(cls, *args, **kwargs):
... ...
... return Wrapper
>>>
>>>
>>> def decorator(cls):
... def wrapper(*args, **kwargs):
... instance = cls.__new__(cls, *args, **kwargs)
... return instance
... return wrapper
>>>
>>>
>>> @decorator
... class MyClass:
... ...
>>>
>>>
>>> my = MyClass()
4.4.3. Example¶
>>> def run(cls):
... def wrapper(*args, **kwargs):
... instance = cls.__new__(cls, *args, **kwargs)
... return instance
... return wrapper
>>>
>>>
>>> @run
... class Astronaut:
... def hello(self, name):
... return f'My name... {name}'
>>>
>>>
>>> astro = Astronaut()
>>> astro.hello('José Jiménez')
'My name... José Jiménez'
4.4.4. Use Case - Logger¶
>>> import logging
>>>
>>>
>>> def logger(cls):
... class Wrapper(cls):
... logger = logging.getLogger(cls.__name__)
... return Wrapper
>>>
>>>
>>> @logger
... class Astronaut:
... pass
>>>
>>>
>>> print(Astronaut.logger)
<Logger Astronaut (WARNING)>
4.4.5. Use Case - Since¶
>>> from datetime import datetime
>>>
>>>
>>> def since(cls):
... class Wrapper(cls):
... _instance_created = datetime.now()
... return Wrapper
>>>
>>>
>>> @since
... class Astronaut:
... pass
>>>
>>>
>>> print(Astronaut._instance_created) #
datetime.datetime(1969, 7, 21, 2, 56, 15)
4.4.6. Use Case - Singleton Func¶
>>> def singleton(cls):
... def wrapper(*args, **kwargs):
... if not hasattr(cls, '_instance'):
... instance = object.__new__(cls, *args, **kwargs)
... setattr(cls, '_instance', instance)
... return getattr(cls, '_instance')
... return wrapper
>>>
>>>
>>> @singleton
... class DatabaseConnection:
... def connect(self):
... print(f'Connecting...')
>>>
>>>
>>> a = DatabaseConnection() # Will create instance
>>> a.connect()
Connecting...
>>>
>>> b = DatabaseConnection() # Will reuse instance
>>> b.connect()
Connecting...
4.4.7. Use Case - Singleton Cls¶
>>> def singleton(cls):
... class Wrapper(cls):
... def __new__(cls, *args, **kwargs):
... if not hasattr(cls, '_instance'):
... instance = object.__new__(cls, *args, **kwargs)
... setattr(cls, '_instance', instance)
... return getattr(cls, '_instance')
... return Wrapper
>>>
>>>
>>> @singleton
... class DatabaseConnection:
... def connect(self):
... print(f'Connecting...')
>>>
>>>
>>> a = DatabaseConnection() # Will create instance
>>> a.connect()
Connecting...
>>>
>>> b = DatabaseConnection() # Will reuse instance
>>> b.connect()
Connecting...