def xform(self, regexp, repl):
        # Do the actual substitution
        s = re.sub(regexp, repl, self._str)

        # The substitution might have generated "empty chunks"
        # (substrings of the form "{}").  Remove them, so they don't
        # interfere with other transformations.
        s = re.sub('\{\}', '', s)

        # Make sure that the transformation was legal.
        if self._debug > 1: self._verify(s, self._debug-2)

        # Commit the transformation.
        self._str = s
Returns a normalized date using a UTC timezone
dataset/ETHPy150Open nltk/nltk/nltk/chunk/regexp.py/ChunkString.xform--crossover with--dataset/ETHPy150Open aws/aws-cli/awscli/customizations/cloudtrail/validation.py/normalize_date