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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 gravatar(self, size=20):
 """ Construct a gravatar image address for the user """

        default = "mm"

        gravatar_url = "//www.gravatar.com/avatar/" + hashlib.md5(self.email.lower()).hexdigest() + "?"
        gravatar_url += urllib.urlencode({'d': default, 's': str(size)})

        return gravatar_url