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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 getone(self, key):
 """ Get one value matching the key, raising a KeyError if multiple values were found. """

        v = self.getall(key)
        if not v:
            raise KeyError('Key not found: %r' % key)
        if len(v) > 1:
            raise KeyError('Multiple values match %r: %r' % (key, v))
        return v[0]