coffeescript advice method combinators a la raganwald, in python

advice.py

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

'''
before = (decoration) ->
           (base) ->
             ->
               decoration.apply(this, arguments)
               base.apply(this, arguments)

after  = (decoration) ->
           (base) ->
             ->
               __value__ = base.apply(this, arguments)
               decoration.apply(this, arguments)
               __value__

around = (decoration) ->
           (base) ->
             (argv...) ->
               callback = => base.apply(this, argv)
               decoration.apply(this, [callback].concat(argv))

provided = (condition) ->
             (base) ->
               ->
                 if condition.apply(this, arguments)
                   base.apply(this, arguments)
'''

def before(decoration):
    def entangle(base):
        def inner(*a, **kw):
            decoration(*a, **kw)
            return base(*a, **kw)
        return inner
    return entangle

def after(decoration):
    def entangle(base):
        def inner(*a, **kw):
            ret = base(*a, **kw)
            decoration(*a, **kw)
            return ret
        return inner
    return entangle

def around(decoration):
    def entangle(base):
        def inner(*a, **kw):
            return decoration(base, *a, **kw)
        return inner
    return entangle

def provided(condition):
    def entangle(base):
        def inner(*a, **kw):
            if condition(*a, **kw):
                return base(*a, **kw)
        return inner
    return entangle

## examples ###################################################################

def say(s):
    print s

def triggers(event):
    @after
    def inner(*a, **kw):
        print "triggering event %r.. (got args %r)" % (event, a)
    return inner

def display_wait():
    outer = {'wait_lvl': 0} #PEP3104
    @around
    def inner(NEXT, *a, **kw):
        outer['wait_lvl'] += 1
        if outer['wait_lvl'] > 0:
            print "showing element"
        ret = NEXT(*a, **kw)
        outer['wait_lvl'] -= 1
        if outer['wait_lvl'] <= 0:
            print "hiding element btw the args were %r" % (a,)
        return ret
    return inner

@triggers("cache:dirty")
def set_heavyweight_prop(prop, val):
    print "set %r to %r" % (prop, val)

@provided(lambda a,b: a > 0 and b > 0)
@before(lambda a,b: say("warning! big calculation about to run"))
@display_wait()
@triggers("cache:dirty")
def recalculate(a, b):
    print "recalculating...", a+b
    return a+b

if __name__ == "__main__":
    print "\n== set_heavyweight_prop =="
    set_heavyweight_prop("pi", 3.14159)

    print "\n== recalculate =="
    recalculate(2, 2)