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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 _link_user(self, userid):
 """Link an existing user to the current Contact """

        # check if we have a selected user from the search-list
        if userid:
            try:
                self.context.setUser(userid)
                self.add_status_message(
                    _("User linked to this Contact"), "info")
            except ValueError, e:
                self.add_status_message(e, "error")
        else:
            self.add_status_message(
                _("Please select a User from the list"), "info")