Python decorators just syntactic sugar? [duplicate]

Question

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Understanding Python decorators

I am quite new on using Python decorators and from what I understand on my first impression that they are just syntactic sugar.

Is there a more profound use of them for more complex uses ?

Answer 1

Yes it is syntactic sugar. Everything can be achieved without them, but with a few more lines of code. But it helps you write more concise code.

Examples:

from functools import wraps  def requires_foo(func):     @wraps(func)     def wrapped(self, *args, **kwargs):         if not hasattr(self, 'foo') or not self.foo is True:             raise Exception('You must have foo and be True!!')         return func(self, *args, **kwargs)     return wrapped  def requires_bar(func):     @wraps(func)     def wrapped(self, *args, **kwargs):         if not hasattr(self, 'bar') or not self.bar is True:             raise Exception('You must have bar and be True!!')         return func(self, *args, **kwargs)     return wrapped  class FooBar(object):      @requires_foo                 # Make sure the requirement is met.     def do_something_to_foo(self):         pass 

We could also chain/stack the decorators on top of each other.

class FooBar(object):     @requires_bar     @requires_foo                 # You can chain as many decorators as you want     def do_something_to_foo_and_bar(self):         pass 

OK, we could end up with lots and lots of decorators on top of each other.

I know! I'll write a decorator that applies other decorators.

So we could do this:

def enforce(requirements):     def wrapper(func):         @wraps(func)         def wrapped(self, *args, **kwargs):             return func(self, *args, **kwargs)         while requirements:             func = requirements.pop()(func)         return wrapped     return wrapper  class FooBar(object):     @enforce([reguires_foo, requires_bar])     def do_something_to_foo_and_bar(self):         pass 

This is a small sample just to play with.

Answer 2

I really like the decorator syntax because it makes code uber explicit

For example, in Django there's this login_required decorator: https://docs.djangoproject.com/en/dev/topics/auth/#django.contrib.auth.decorators.login_required

To inject the @login_required behavior for a function/view, all you gotta do is attach the decorator to it (as opposed to putting if: ... else: ... control expressions everywhere etc. )

Read the PEP!

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

it has losta history on the language decisions that were made, and why