Writes bus data to file.

def write_bus_data(self, file, padding="    "):
        """ Writes bus data to file.
        """
        for bus in self.case.buses:
            attrs = ['%s="%s"' % (k, v) for k, v in self.bus_attr.iteritems()]
#            attrs.insert(0, 'label="%s"' % bus.name)
            attr_str = ", ".join(attrs)

            file.write("%s%s [%s];\n" % (padding, bus.name, attr_str))