python decorators

Decorators allow us to 'wrap' functions with custom functionality.

Decorators can be thought of as functions which take a function as a parameter, and return a new function which wraps the passed in function with some new functionality.

def  decorate(func):
    def wrapped():
        print 'before'
        func()
        print 'after'
    return wrapped

Let's say we have a function foo() which we want to decorate; we use the following syntax:


@decorate
def foo():
    print 'foo'


Now, calling foo() results in the following:

    before
    foo
    after

Here is a base class which can be extended to add custom before and after functionality

class decorate:
    """
    A decorator which can be extended to allow custom before and after 
    functionality to be called around a function
    """
    def before(self):
        pass

    def after(self):
        pass

    def __call__(self,func):
        def new_f(*args,**kw):
            self.before()
            try:
                res = func(*args,**kw)
                self.after()
                return res
            except:
                self.after()
                raise
        return new_f

Extend this class and override before and after:

class print_before_after(decorate):

    def before(self):

        print 'before'

    def after(self):

        print 'after'

@print_before_after() # note here we can pass args 

def foo():

    print 'foo'