def write_file(self, filename):
        """Write the coverage data to `filename`."""

        # Create the file data.
        data = {}

        data['lines'] = self.line_data()
        arcs = self.arc_data()
        if arcs:
            data['arcs'] = arcs

        if self.collector:
            data['collector'] = self.collector

        if self.debug and self.debug.should('dataio'):
            self.debug.write("Writing data to %r" % (filename,))

        # Write the pickle to the file.
        fdata = open(filename, 'wb')
        try:
            pickle.dump(data, fdata, 2)
        finally:
            fdata.close()
Write the coverage data to `filename`.