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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 social_media_profile(self, site: Optional[SocialNetwork] = None) -> str: """Generate profile for random social network. :return: Profile in some network. :Example: http://facebook.com/some_user """

        key = self._validate_enum(site, SocialNetwork)
        website = SOCIAL_NETWORKS[key]
        url = 'https://www.' + website
        return url.format(self.username())