问题
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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 ?
回答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.
回答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
来源：https://stackoverflow.com/questions/12295974/python-decorators-just-syntactic-sugar