Question

I have login_required decorator as follows:

def login_required(function):
  """ Decorator to check Logged in users."""
  def check_login(self, *args, **kwargs):
    if not self.auth.get_user_by_session():
      self.redirect('/_ah/login_required')
    else:
      return function(self, *args, **kwargs)
  return check_login

Now I have a Page (which is rendered by a seperate Handler) where I have an option for users to upload image which can be viewed both by guests and users. As soon as the form is posted it is handled by another Handler which uses the @login_required decorator.

What I want to achieve is passing a continue_url variable that I can use in the check_login function while redirecting so that the user gets redirected back to the same page after logging in.

Answer 1

So basically, it sounds like you want to pass an argument to the decorator when you use it. Python does support this. The basic idea is that @decorated(argument) def foo(...) is equivalent to def foo(...); foo = decorated(argument)(foo).

So you need to make decorated be something such that decorated(argument) can decorate foo. There are several recipes for this. Here’s one – make decorated a class with a __call__ method, so that decorated(argument) is a callable object that stores argument and uses it when called:

class decorator(object):
    def __init__(argument):
        self.argument = argument

    def __call__(self, wrapped):
        def wrapper(args_for_wrapped):
            do_something_with(self.argument)
            wrapped(args_for_wrapped)
            whatever_else_this_needs_to_do()
        return wrapper

This can also be achieved with a plain function (and an additional level of nesting), with tricks involving functools.partial etc.