Inheritance problem ?

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  • tooper
    #1

    Inheritance problem ?

    Hello all,

    I'm trying to implement a common behavior for some object that can be
    read from a DB or (when out of network) from an XML extract of this DB.
    I've then wrote 2 classes, one reading from XML & the other from the
    DB, both inheritating from a common one where I want to implement
    several common methods.
    Doing this, I've come to some behaviour I can't explain to myself,
    which I've reproduced in the example bellow :

    -----

    class myfather:
    def __repr__(self):
    return "\t a="+self.a+"\n\ t b="+self.b

    class mychilda(myfath er):
    def __init__(self,a ):
    self.a= a
    def __getattr__(sel f,name):
    return "Undefined for mychilda"

    class mychildb(myfath er):
    def __init__(self,b ):
    self.b= b
    def __getattr__(sel f,name):
    return "Undefined for mychildb"

    a= mychilda("a")
    b= mychildb("b")

    print "a:\n"+str( a)
    print "b:\n"+str( b)

    -----

    I was expecting to get :

    a:
    a= a
    b= Undefined for mychilda
    b:
    a= Undefined for mychildb
    b= b

    but I get the following error :

    File "/home/thierry/mytest.py", line 20, in ?
    print "a:\n"+str( a)
    TypeError: 'str' object is not callable

    Could someone explain me what I missed ?

    Thanks in advance !

    Tags: None
    • db
      #2
      Re: Inheritance problem ?

      On Wed, 24 Aug 2005 03:34:36 -0700, tooper wrote:
      [color=blue]
      > Hello all,
      >
      > I'm trying to implement a common behavior for some object that can be
      > read from a DB or (when out of network) from an XML extract of this DB.
      > I've then wrote 2 classes, one reading from XML & the other from the
      > DB, both inheritating from a common one where I want to implement
      > several common methods.
      > Doing this, I've come to some behaviour I can't explain to myself,
      > which I've reproduced in the example bellow :
      >
      > -----
      >
      > class myfather:
      > def __repr__(self):
      > return "\t a="+self.a+"\n\ t b="+self.b
      >
      > class mychilda(myfath er):
      > def __init__(self,a ):
      > self.a= a
      > def __getattr__(sel f,name):
      > return "Undefined for mychilda"
      >
      > class mychildb(myfath er):
      > def __init__(self,b ):
      > self.b= b
      > def __getattr__(sel f,name):
      > return "Undefined for mychildb"
      >
      > a= mychilda("a")
      > b= mychildb("b")
      >
      > print "a:\n"+str( a)
      > print "b:\n"+str( b)
      >
      > -----
      >
      > I was expecting to get :
      >
      > a:
      > a= a
      > b= Undefined for mychilda
      > b:
      > a= Undefined for mychildb
      > b= b
      >
      > but I get the following error :
      >
      > File "/home/thierry/mytest.py", line 20, in ?
      > print "a:\n"+str( a)
      > TypeError: 'str' object is not callable
      >
      > Could someone explain me what I missed ?
      >
      > Thanks in advance ![/color]

      try new style classes.
      class myfather(object ):

      see http://users.rcn.com/python/download/Descriptor.htm

      HTH Arjen



        Comment

        • jitya
          #3
          Re: Inheritance problem ?

          tooper wrote:[color=blue]
          > Hello all,
          >
          > I'm trying to implement a common behavior for some object that can be
          > read from a DB or (when out of network) from an XML extract of this DB.
          > I've then wrote 2 classes, one reading from XML & the other from the
          > DB, both inheritating from a common one where I want to implement
          > several common methods.
          > Doing this, I've come to some behaviour I can't explain to myself,
          > which I've reproduced in the example bellow :
          >
          > -----
          >
          > class myfather:
          > def __repr__(self):
          > return "\t a="+self.a+"\n\ t b="+self.b
          >
          > class mychilda(myfath er):
          > def __init__(self,a ):
          > self.a= a
          > def __getattr__(sel f,name):
          > return "Undefined for mychilda"
          >
          > class mychildb(myfath er):
          > def __init__(self,b ):
          > self.b= b
          > def __getattr__(sel f,name):
          > return "Undefined for mychildb"
          >
          > a= mychilda("a")
          > b= mychildb("b")
          >
          > print "a:\n"+str( a)
          > print "b:\n"+str( b)
          >
          > -----
          >
          > I was expecting to get :
          >
          > a:
          > a= a
          > b= Undefined for mychilda
          > b:
          > a= Undefined for mychildb
          > b= b
          >
          > but I get the following error :
          >
          > File "/home/thierry/mytest.py", line 20, in ?
          > print "a:\n"+str( a)
          > TypeError: 'str' object is not callable
          >
          > Could someone explain me what I missed ?
          >
          > Thanks in advance ![/color]

          hi I am got python 2.4 and changed "class myfather"
          to new style classes "class myfather(object )" it worked.
          here is the output :

          a:
          a=a
          b=Undefined for mychilda
          b:
          a=Undefined for mychildb
          b=b

          But i myself still need explaination ;)

          regards
          jitu

            Comment

            • tooper
              #4
              Re: Inheritance problem ?

              Thanks, at least makes it running !
              I'll have to teach myself to move to this new style classes by default
              anyway...

                Comment

                • jitya
                  #5
                  Re: Inheritance problem ?

                  The stuff on Descriptor.htm was really good .

                  Thanks

                    Comment

                    • tooper
                      #6
                      Re: Inheritance problem ?

                      Not always easy to follow but great !
                      Using __str__ instead of __repr__ makes it work also with old style
                      (thanks to Simon Brunning for suggesting it, and with your link I even
                      now understand why !)

                        Comment

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