Re: [Tutor] Problem with calling class methods stored in a list

[Tobias M.]

Peter Otten wrote:
You are right; the misunderstanding is that I wasn't advertising the above
"fancy" solution (which is buggy, btw).
Yes, I wasn't sure about the irony in you last post ;)
Peter Otten wrote:

I have now implemented what I had in mind with the protocol to function name
mapping, and I think /that/ is reasonably complex. I'm using instance
methods in the demo, but it should work with class methods as well.

class Error(Exception):
     def __init__(self, protocol):
         Exception.__init__(self, self.template.format(protocol))

class UnknownProtocolError(Error):
     template = "Unknown protocol {}"

class ProtocolNotSupportedError(Error):
     template = "Protocol {} not supported"

FOO = (42, 17)
BAR = (1, 2)
BAZ = (3, 4)
HAM = (4, 5)
SPAM = (5, 6)

class HandlersBase(object):
     protocol_to_methodname = {
         FOO: "foo",
         BAR: "bar",
         BAZ: "baz",
         HAM: "ham",
         }
     def get_handler(self, protocol):
         try:
             methodname = self.protocol_to_methodname[protocol]
         except KeyError:
             raise UnknownProtocolError(protocol)
         
         method = getattr(self, methodname, None)
         if method is None:
             raise ProtocolNotSupportedError(protocol)
         return method

class A(HandlersBase):
     def foo(self): print "A.foo"
     def bar(self): print "A.bar"
     def baz(self): print "A.baz"
     
class B(A):
     def bar(self): print "B.bar"
     baz = None # hide parent implementation

if __name__ == "__main__":

     for Class in A, B:
         inst = Class()
         print "---", Class.__name__, "---"
         for protocol in FOO, BAR, BAZ, SPAM:
             try:
                 inst.get_handler(protocol)()
             except Error as err:
                 print err
Thanks for the code! It's very similar to what I implemented but more 
flexible regarding inheritance.
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