New use for __ names! (Re: Is there a pattern...)

[Greg Ewing]

"Magnus L. Hetland" wrote:
> 
> So I started to wonder - is there an intelligent design pattern that
> addresses this problem, i.e. methods that should only be called from a
> specific class or a specific set of objects or something?

How's this for a sneaky hack which shamelessly misuses
the "__" name mangling mechanism:

class Foo:
    
    def _Blarg__secret(self):
        print "secret method called"

class Blarg:
    
    def doit(self, foo):
        foo.__secret()

class Impostor:
    
    def doit(self, foo):
        foo.__secret()

f = Foo()
b = Blarg()
i = Impostor()

try:
    b.doit(f)
    i.doit(f)
except AttributeError:
    print "impostor detected"


################ Output ###################

secret method called
impostor detected

###########################################

There's-more-than-one-use-for-the-skin-of-a-cat,
Greg








 (Somewhat
> like friend classes in C++, I guess - if I don't remember it all
> wrong...)
> 
> Of course, you *could* just appeal to the programmers conscience and
> tell him not to call the methods anywhere else, but...
> 
> --
> 
>   Magnus              Making no sound / Yet smouldering with passion
>   Lie          The firefly is still sadder / Than the moaning insect
>   Hetland                                       : Minamoto Shigeyuki