Returns a callable that will encode C{data} to C{self.stream}. If
        C{data} is unencodable, then C{None} is returned.

def getTypeFunc(self, data):
        """
        Returns a callable that will encode C{data} to C{self.stream}. If
        C{data} is unencodable, then C{None} is returned.
        """
        if data is None:
            return self.writeNull

        t = type(data)

        # try types that we know will work
        if t is str or issubclass(t, str):
            return self.writeBytes
        if t is unicode or issubclass(t, unicode):
            return self.writeString
        elif t is bool:
            return self.writeBoolean
        elif t is float:
            return self.writeNumber
        elif t in python.int_types:
            return self.writeNumber
        elif t in (list, tuple):
            return self.writeList
        elif isinstance(data, (list, tuple)):
            return self.writeSequence
        elif t is types.GeneratorType:
            return self.writeGenerator
        elif t is pyamf.UndefinedType:
            return self.writeUndefined
        elif t in (datetime.date, datetime.datetime, datetime.time):
            return self.writeDate
        elif xml.is_xml(data):
            return self.writeXML

        # check for any overridden types
        for type_, func in pyamf.TYPE_MAP.iteritems():
            try:
                if isinstance(data, type_):
                    return _CustomTypeFunc(self, func)
            except TypeError:
                if python.callable(type_) and type_(data):
                    return _CustomTypeFunc(self, func)

        # now try some types that won't encode
        if t in python.class_types:
            # can't encode classes
            return None
        elif isinstance(data, python.func_types):
            # can't encode code objects
            return None
        elif isinstance(t, types.ModuleType):
            # cannot encode module objects
            return None

        # well, we tried ..
        return self.writeObject