reaching hidden methods + casting

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  • per9000
    #1

    reaching hidden methods + casting

    Hi,
    can I reach a hidden method when doing ugly inheritance in python?
    >>class A:
    .... def spin(self, n): print "A", n
    ....
    >>class B:
    .... def spin(self, m): print "B", m
    ....
    >>class C(A,B):
    .... def spin(self, k): print "C", k
    ....
    >>myC = C()
    >>dir(myC)
    ['__doc__', '__module__', 'spin']

    In f.x. the C-family of languages I guess something like this would
    call B.spin:
    ((B)myC).spin(" Lancelot"); // almost forgot the ';'

    Please correct me I am wrong (which I likely am) but as I understand
    it this example calls the constructor of int instead of casting it,
    right?
    >>leet = int('1337')
    >>leet
    1337

    So is there another way of digging into the past of a class? Or can/
    should I create constructors for the classes A, B and C that takes
    objects of the other classes?

    Or should I have thought about getting unique names before I
    implemented the ugly inheritance graph?

    /Per

    --

    Per Erik Strandberg
    blog: http://www.pererikstrandberg.se/blog/

    Tags: None
    • Gabriel Genellina
      #2
      Re: reaching hidden methods + casting

      En Thu, 12 Apr 2007 04:18:19 -0300, per9000 <per9000@gmail. comescribió:
      Hi,
      can I reach a hidden method when doing ugly inheritance in python?
      >
      >>>class A:
      ... def spin(self, n): print "A", n
      ...
      >>>class B:
      ... def spin(self, m): print "B", m
      ...
      >>>class C(A,B):
      ... def spin(self, k): print "C", k
      ...
      >>>myC = C()
      >>>dir(myC)
      ['__doc__', '__module__', 'spin']
      >
      In f.x. the C-family of languages I guess something like this would
      call B.spin:
      ((B)myC).spin(" Lancelot"); // almost forgot the ';'
      Try this in Python:
      B.spin(myC, "Lancelot")

      You can't ask the instance for myC.spin because that would retrieve
      C.spin; you need B.spin instead. But if you get it this way, it's not
      associated to a specific instance, so you must pass myC explicitely
      (becoming 'self').
      Please correct me I am wrong (which I likely am) but as I understand
      it this example calls the constructor of int instead of casting it,
      right?
      >>>leet = int('1337')
      >>>leet
      1337
      Yes.
      So is there another way of digging into the past of a class? Or can/
      should I create constructors for the classes A, B and C that takes
      objects of the other classes?
      No need for that. And usually, that's not what you want either: you're
      creating a *different* object that way, not calling a (shadowed) method on
      an existing object.
      Or should I have thought about getting unique names before I
      implemented the ugly inheritance graph?
      Perhaps...

      --
      Gabriel Genellina

        Comment

        • Bruno Desthuilliers
          #3
          Re: reaching hidden methods + casting

          per9000 a écrit :
          Hi,
          can I reach a hidden method when doing ugly inheritance in python?
          >
          >>>class A:
          ... def spin(self, n): print "A", n
          ...
          >>>class B:
          ... def spin(self, m): print "B", m
          ...
          >>>class C(A,B):
          ... def spin(self, k): print "C", k
          ...
          >>>myC = C()
          >>>dir(myC)
          ['__doc__', '__module__', 'spin']
          >
          In f.x. the C-family of languages I guess something like this would
          call B.spin:
          ((B)myC).spin(" Lancelot"); // almost forgot the ';'
          B.spin(myC, "lancelot")

          In Python, the syntax:
          some_instance.s ome_method(para m)

          is syntactic sugar for
          SomeClass.some_ method(some_ins tance, param)

          (assuming isinstance(some _instance, SomeClass) == True)
          Please correct me I am wrong (which I likely am) but as I understand
          it this example calls the constructor of int instead of casting it,
          right?
          >>>leet = int('1337')
          >>>leet
          1337
          There's nothing like "casting" in Python - it would be meaningless in a
          dynamically typed language. The above example does not "cast" a string
          to an int, it creates an int - you have two distinct objects, whereas
          with casting you have two representations of the same object.
          Or should I have thought about getting unique names before I
          implemented the ugly inheritance graph?
          This is a design question, and we don't have enough context to answer it.

            Comment

            • per9000
              #4
              Re: reaching hidden methods + casting

              On 12 Apr, 09:42, "Gabriel Genellina" <gagsl-...@yahoo.com.a rwrote:
              >
              <snip>
              >
              In f.x. the C-family of languages I guess something like this would
              call B.spin:
              ((B)myC).spin(" Lancelot"); // almost forgot the ';'
              >
              Try this in Python:
              B.spin(myC, "Lancelot")
              >
              >
              <snip>
              >

              Thanks, that was exactly the insight i needed.

              /Per

              --

              Per Erik Strandberg
              blog: http://www.pererikstrandberg.se/blog/

                Comment

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