def download(self, overwrite=True):
        """
        Download the zipcodes CSV file. If ``overwrite`` is set to False, the
        file won't be downloaded if it already exists.
        """
        if overwrite or not os.path.exists(self.file_path):
            _, f = tempfile.mkstemp()
            try:
                urlretrieve(self.DOWNLOAD_URL, f)
                extract_csv(f, self.file_path)
            finally:
                os.remove(f)
Download the zipcodes CSV file. If ``overwrite`` is set to False, the
        file won't be downloaded if it already exists.