Extending base class methods

[henrikpierrou at hotmail.com]

Hi,

I am trying to extend an overridden base class method (printer) by
printing some extra fields and then calling the base class method.
Extract from the python tutorial:

'An overriding method in a derived class may in fact want to extend
rather than simply replace the base class method of the same name.
There is a simple way to call the base class method directly: just call
"BaseClassName.methodname(self, arguments)". '


Any ideas why this does not work? I get the error "TypeError: unbound
method printer() must be called with Field_Collection instance as first
argument (got MSD instance instead)"):


#=====================================================================================
class Field_Collection:
    fieldList = []

    def add(self, name, size, compression, responseValue, value,
description):
        self.fieldList.append( Field(name, size, compression,
responseValue, value, description) )

    def update(self):
        print "updating field"

    def get(self):
        print "getting field"

    def printer(self):
        for x in self.fieldList:
            x.printer()


#=====================================================================================


class MSD(Field_Collection):
    standard = ""
    decField = ""

    def printer(self):
        print "Standard: " + self.standard
        print "decField: " + self.decField
        Field_Collection.printer(self)

#=====================================================================================

w2k, python 2.3