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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 register_get(self, regex, callback):
 """ Register a regex for processing HTTP GET requests. If the callback is None, any existing registration is removed. """

        if callback is None:                                                                    # pragma: no cover
            if regex in self.get_registrations:
                del self.get_registrations[regex]
        else:
            self.get_registrations[regex] = (re.compile(regex), callback)