'Return a list of file identifiers for the files that make up
this corpus.
:param filetype: If specified, then ``filetype`` indicates that
only the files that have the given type should be
returned.  Accepted values are: ``txt``, ``wrd``, ``phn``,
``wav``, or ``metadata``,'

def fileids(self, filetype=None):

    if (filetype is None):
        return CorpusReader.fileids(self)
    elif (filetype in (u'txt', u'wrd', u'phn', u'wav')):
        return [(u'%s.%s' % (u, filetype)) for u in self._utterances]
    elif (filetype == u'metadata'):
        return [u'timitdic.txt', u'spkrinfo.txt']
    else:
        raise ValueError((u'Bad    value    for    filetype:    %r' % filetype))
