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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add(self, pat, fun):
 r"""Add a pattern and replacement. The pattern must not contain capturing groups. The replacement might be either a string template in which \& will be replaced with the match, or a function that will get the matching text as argument. It does not get match object, because capturing is forbidden anyway. """

        self._pat = None
        self._pats.append(pat)
        self._funs.append(fun)