'VTK files can be either ASCII or binary, with two different
styles of file formats: legacy or XML.  We\'ll assume if the
file contains a valid VTK header, then it is a valid VTK file.'

def sniff(self, filename):

    with open(filename, 'r') as fh:
        if self._is_vtk_header(fh, self.subtype):
            return True
        return False
    return False
