<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def filter_chars(self, chars=u""):
 """ Return a new IPAString, containing only the IPA characters specified by the ``chars`` string. Valid values for ``chars`` are: * ``consonants`` or ``cns`` * ``vowels`` or ``vwl`` * ``letters`` or ``cns_vwl`` * ``cns_vwl_pstr`` or ``cvp`` * ``cns_vwl_pstr_long`` or ``cvpl`` * ``cns_vwl_str`` or ``cvs`` * ``cns_vwl_str_len`` or ``cvsl`` * ``cns_vwl_str_len_wb`` or ``cvslw`` * ``cns_vwl_str_len_wb_sb`` or ``cvslws`` :rtype: IPAString """

        if chars in [u"cns", u"consonants"]:
            return self.consonants
        elif chars in [u"vwl", u"vowels"]:
            return self.vowels
        elif chars in [u"cns_vwl", u"letters"]:
            return self.letters
        elif chars in [u"cns_vwl_pstr", u"cvp"]:
            return self.cns_vwl_pstr
        elif chars in [u"cns_vwl_pstr_long", u"cvpl"]:
            return self.cns_vwl_pstr_long
        elif chars in [u"cns_vwl_str", u"cvs"]:
            return self.cns_vwl_str
        elif chars in [u"cns_vwl_str_len", u"cvsl"]:
            return self.cns_vwl_str_len
        elif chars in [u"cns_vwl_str_len_wb", u"cvslw"]:
            return self.cns_vwl_str_len_wb
        elif chars in [u"cns_vwl_str_len_wb_sb", u"cvslws"]:
            return self.cns_vwl_str_len_wb_sb
        return self