def parse(self, filenames):
        """
        Read and parse a filename or a list of filenames.
        Files that cannot be opened are ignored. A single filename may also be given.

        Return: list of successfully read files.
        """
        filenames = list_strings(filenames)

        read_ok = []
        for fname in filenames:
            try:
                fh = open(fname)
            except IOError:
                logger.warning("Cannot open file %s" % fname)
                continue

            try:
                self._read(fh, fname)
                read_ok.append(fname)

            except self.Error as e:
                logger.warning("exception while parsing file %s:\n%s" % (fname, str(e)))
                continue

            finally:
                fh.close()

        # Add read_ok to the list of files that have been parsed.
        self._filenames.extend(read_ok)
        return read_ok