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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 urls(self, version=None):
 """Returns all URLS that are mapped to this interface"""

        urls = []
        for base_url, routes in self.api.http.routes.items():
            for url, methods in routes.items():
                for method, versions in methods.items():
                    for interface_version, interface in versions.items():
                        if interface_version == version and interface == self:
                            if not url in urls:
                                urls.append(('/v{0}'.format(version) if version else '') + url)
        return urls