color version - PET: Python Entre Todos - Python Argentina

A first example:
Identity:
def identity(C):
return C
Returns the same class we are decorating.
>>> @identity
... class A(object):
... pass
...
>>> A()
Change a class totally:
return X
>>> @replace_with_X
... class MyClass():
... pass
...
>>> MyClass
In the previous case we see that the class was changed completely for a brand new
different class.
Instance:
def instantiate(C):
return C()
def abuse(C):
return "hello"
>>> @abuse
... class A(object):
... pass
...
>>> A()
Traceback (most recent call last):
File "", line 1, in
TypeError: 'str' object is not callable
>>> A
'hello'
Similar to one of the examples you’ve read at the beginning, this example shows us that
a decorator’s return has to have a similar interface as the object we are decorating, that
way it makes more sense to change the use of the original object, for a changed one.
Replace with a new class:
def replace_with_X(C):
class X():
pass
>>> @instantiate
... class MyClass():
... pass
...
>>> MyClass
As last example of class decorators we’ve seen a decorator that once applied, instantiates
the class and links this object to its name. This can be seen as a way to implement the
Singleton design pattern, studied in programming. # wikipedia singleton quote
To finish:
Where can I find decorators
Permissions in Django
@login_required
def my_view(request):
...
URL routing in Bottle