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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 best_match( self, req, working_set, installer=None, replace_conflicting=False):
 """Find distribution best matching `req` and usable on `working_set` This calls the ``find(req)`` method of the `working_set` to see if a suitable distribution is already active. (This may raise ``VersionConflict`` if an unsuitable version of the project is already active in the specified `working_set`.) If a suitable distribution isn't active, this method returns the newest distribution in the environment that meets the ``Requirement`` in `req`. If no suitable distribution is found, and `installer` is supplied, then the result of calling the environment's ``obtain(req, installer)`` method will be returned. """

        try:
            dist = working_set.find(req)
        except VersionConflict:
            if not replace_conflicting:
                raise
            dist = None
        if dist is not None:
            return dist
        for dist in self[req.key]:
            if dist in req:
                return dist
        # try to download/install
        return self.obtain(req, installer)