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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 current transformation, which can be used to retrieve the file. If security is enabled, signature and policy parameters will be included *returns* [String] ```python transform = client.upload(filepath='/path/to/file') transform.url() # https://cdn.filestackcontent.com/TRANSFORMS/FILE_HANDLE ``` """

        return utils.get_transform_url(
            self._transformation_tasks, external_url=self.external_url,
            handle=self.handle, security=self.security, apikey=self.apikey
        )