In Python, what are some examples when decorators greatly simplify the task?

Question

Trying to find examples of when decorators can be really useful, and when not so much. Sample code is evaluated.

Answer 1

The easiest way to understand the usefulness of decorators is to see a few examples. Here is one, for example:

Suppose you are studying some kind of code and want to understand when and how a function is called. You can use the decorator to change the function, so it prints some debugging information each time the function is called:

import functools
def trace(f):
    '''This decorator shows how the function was called'''
    @functools.wraps(f)
    def wrapper(*arg,**kw):            
        arg_str=','.join(['%r'%a for a in arg]+['%s=%s'%(key,kw[key]) for key in kw])
        print "%s(%s)" % (f.__name__, arg_str)
        return f(*arg, **kw)
    return wrapper

@trace
def foo(*args):
    pass


for n in range(3):
    foo(n)

prints:

# foo(0)
# foo(1)
# foo(2)

If you only wanted to trace one function foo, you could, of course, add the code more simply to the definition foo:

def foo(*args):
    print('foo({0})'.format(args))

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Answer 2

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Answer 3

@property :

@property
def count(self):
    return self._events

:

def _get_count(self):
    return self._events

count = property(_get_count)

Answer 4

API AppEngine @login_required decorator, :

class MyPage(webapp.RequestHandler):
    @login_required
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write("Hello, world!")

:

class MyPage(webapp.RequestHandler):
    def get(self):
        user = users.get_current_user()
        if not user:
            return self.redirect(users.create_login_url(self.request.uri))

        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write("Hello, world!")

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    @classmethod
    def foo(cls):
        return id(cls)

:

class Bar(object):
    def foo(cls):
        return id(cls)
    foo = classmethod(foo)

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Answer 5

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