将两个python装饰器合二为一

Question

Here are two decorators I'd like to combine as they are pretty similar, the difference is how a not authenticated user is handled. I'd prefer to have one single decorator that I can call with an argument.

# Authentication decorator for routes
# Will redirect to the login page if not authenticated
def requireAuthentication(fn):
    def decorator(**kwargs):
        # Is user logged on?
        if "user" in request.session:
            return fn(**kwargs)
        # No, redirect to login page
        else:
            redirect('/login?url={0}{1}'.format(request.path, ("?" + request.query_string if request.query_string else '')))
    return decorator

# Authentication decorator for routes
# Will return an error message (in JSON) if not authenticated
def requireAuthenticationJSON(fn):
    def decorator(**kwargs):
        # Is user logged on?
        if "user" in request.session:
            return fn(**kwargs)
        # No, return error
        else:
            return {
                "exception": "NotAuthorized",
                "error" : "You are not authorized, please log on"
            }
    return decorator

And currently I'm using these decorators for specific routes, eg

@get('/day/')
@helpers.requireAuthentication
def day():
    ...

@get('/night/')
@helpers.requireAuthenticationJSON
def night():
    ...

I'd much more prefer this:

@get('/day/')
@helpers.requireAuthentication()
def day():
    ...

@get('/night/')
@helpers.requireAuthentication(json = True)
def night():
    ...

I'm on python 3.3 using the Bottle framework. Is it possible to do what I want? How?

Answer 1

Just add another wrapper to capture the json parameter:

def requireAuthentication(json=False):
    def decorator(fn):
        def wrapper(**kwargs):
            # Is user logged on?
            if "user" in request.session:
                return fn(**kwargs)

            # No, return error
            if json:
                return {
                    "exception": "NotAuthorized",
                    "error" : "You are not authorized, please log on"
                }
            redirect('/login?url={0}{1}'.format(request.path, ("?" + request.query_string if request.query_string else '')))
        return wrapper
    return decorator

I've renamed your original requireAuthentication function to decorator (because that is what that function did, it decorated fn ) and renamed the old decorator to wrapper , the usual convention.

Whatever you put after the @ is an expression, evaluated first to find the actual decorator function. @helpers.requireAuthentication() means you want to call requireAuthentication and it's return value is then used as the actual decorator for the function the @ line applies to.

Answer 2

You can create wrapper for both of these decorators:

def requireAuthentication(json=False):
    if json:
        return helpers.requireAuthenticationJSON
    else:
        return helpers.requireAuthentication

Or

import functools
# Authentication decorator for routes
# Will redirect to the login page if not authenticated
def requireAuthentication(json=False):
    def requireAuthentication(fn):
        @functools.wraps(fn)
        def decorator(*args, **kwargs):
            # Is user logged on?
            if "user" in request.session:
                return fn(*args, **kwargs)
            if json:
                 return {
                "exception": "NotAuthorized",
                "error" : "You are not authorized, please log on"
            }
            return redirect('/login?url={0}{1}'.format(request.path, 
                                                       ("?" + request.query_string if request.query_string else '')))
        return decorator
    return requireAuthentication