def __call__(self,*args, **kwargs):
        '''execute the samtools command
        retval, stderr, stdout = csamtools._samtools_dispatch( self.dispatch, args )
        if retval: raise SamtoolsError( "\n".join( stderr ) )
        self.stderr = stderr
        # samtools commands do not propagate the return code correctly.
        # I have thus added this patch to throw if there is output on stderr.
        # Note that there is sometimes output on stderr that is not an error,
        # for example: [sam_header_read2] 2 sequences loaded.
        # Ignore messages like these
        stderr = [x for x in stderr
                  if not (x.startswith( "[sam_header_read2]" ) or
                          x.startswith("[bam_index_load]") or
                          x.startswith("[bam_sort_core]") or \
                          x.startswith("[samopen] SAM header is present"))]
        if stderr: raise SamtoolsError( "\n".join( stderr ) )
        # call parser for stdout:
        if not kwargs.get("raw") and stdout and self.parsers:
            for options, parser in self.parsers:
                for option in options: 
                    if option not in args: break
                    return parser(stdout)

        return stdout
 def usage(self):
     '''return the samtools usage information for this command'''
     retval, stderr, stdout = csamtools._samtools_dispatch( self.dispatch )
     return "".join(stderr)