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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 url(self):
 """ Returns the URL for the instance, which can be used to retrieve, delete, and overwrite the file. If security is enabled, signature and policy parameters will be included, *returns* [String] ```python filelink = client.upload(filepath='/path/to/file') filelink.url # https://cdn.filestackcontent.com/FILE_HANDLE ``` """

        return get_url(CDN_URL, handle=self.handle, security=self.security)