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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 download_or_copy_if_necessary( self, path_or_url, download_if_missing=False, overwrite=False):
 """ Download a remote file or copy Get the local path to a possibly remote file. Download if file is missing from the cache directory and `download_if_missing` is True. Download even if local file exists if both `download_if_missing` and `overwrite` are True. If the file is on the local file system then return its path, unless self.copy_local_to_cache is True, and then copy it to the cache first. Parameters path_or_url : str download_if_missing : bool, optional Download files if missing from local cache overwrite : bool, optional Overwrite existing copy if it exists """

        assert path_or_url, "Expected non-empty string for path_or_url"
        if self.is_url_format(path_or_url):
            return self._download_if_necessary(
                path_or_url,
                download_if_missing,
                overwrite)
        else:
            return self._copy_if_necessary(path_or_url, overwrite)