coffeescript decorator examples a la raganwald, but in python

decorators.py

#http://news.ycombinator.com/item?id=4439352

def has_permission_to(user, verb, subj):
    if user == "steve" and verb == "write":
        return True
    elif user == "alice" and verb == "read":
        return True
    return False

def current_user():
    import random
    return random.choice(["alice", "steve"])

## advice / decorators ########################################################

def with_permission(verb, subj):
    def entangle(f):
        def inner(*a, **kw):
            u = current_user()
            if has_permission_to(u, verb, subj):
                return f(*a, **kw)
            else:
                return "error: %r does not have %r access to %r" % (u, verb, subj)
        return inner
    return entangle

def debug_entry_and_exit(msg):
    def entangle(f):
        def inner(*a, **kw):
            print "[debug]", "entering", msg
            ret = f(*a, **kw)
            print "[debug]", "leaving", msg
            return ret
        return inner
    return entangle

## widget views using some framework... #######################################

class FrameworkView(object):
    def edit(self, page):
        return "stub for editing %r" % page

    def view(self, page):
        return "stub for viewing %r" % page

class WidgetView(FrameworkView):
    @debug_entry_and_exit("edit")
    @with_permission("write", "widget")
    def edit(self, page):
        return "you can edit %r" % page

    @debug_entry_and_exit("view")
    @with_permission("read", "widget")
    def view(self, page):
        return "you can view %r" % page

class RaganwaldWidgetViewOne(FrameworkView):
    '''Same as WidgetView but without python's @decorator syntax.

    Somewhat equivalent to the coffeescript version, but instead of decorating the multi-line
    anonymous function, we first give that body of the function a name, then decorate that.
    '''

    def edit(self, page):
        def body(self, page):
            return "you can edit %r" % page
        return (
            debug_entry_and_exit("edit")(
            with_permission("write", "widget")(
            body
        )))(self, page)

    def view(self, page):
        def body(self, page):
            return "you can view %r" % page
        return (
            debug_entry_and_exit("view")(
            with_permission("read", "widget")(
            body
        )))(self, page)

class RaganwaldWidgetViewTwo(FrameworkView):
    '''Same as WidgetView but without python's @decorator syntax.

    We apply the decorators to the method from the body of the class intead of within the
    method itself. This is what people were doing before the @ syntax existed; the @ syntax
    isn't really "magic", it's just sugar for this pattern (def f(x)...; f = deco(f)).'''

    def edit(self, page):
        return "you can edit %r" % page
    edit = (
        debug_entry_and_exit("edit")(
        with_permission("write", "widget")(
        edit
    )))

    def view(self, page):
        return "you can view %r" % page
    view = (
        debug_entry_and_exit("view")(
        with_permission("read", "widget")(
        view
    )))

class RaganwaldWidgetViewThree(FrameworkView):
    '''Same as WidgetView, without python's @decorator syntax, and using anonymous functions.'''

    edit = (
        debug_entry_and_exit("edit")(
        with_permission("write", "widget")(
        lambda self, page: "you can edit %r" % page #if python had multi-line lambda, this would be equivalent to the coffeescript example
    )))

    view = (
        debug_entry_and_exit("view")(
        with_permission("read", "widget")(
        lambda self, page: "you can view %r" % page
    )))

## main #######################################################################

if __name__ == "__main__":
    ws = [
        WidgetView(),
        RaganwaldWidgetViewOne(),
        RaganwaldWidgetViewTwo(),
        RaganwaldWidgetViewThree(),
    ]

    for w in ws:
        print "\n\n== %s ==\n" % w.__class__.__name__
        for name in "red blue".split():
            print w.edit(name)
            print w.view(name)
            print ""