from pathlib import Path def change_file_extension_with_pathlib(filename, new_extension): path_object = Path(filename) new_filename = path_object.with_suffix('.' + new_extension) return new_filenamefrom pathlib import Path filename = Path("/some/dir/to/file_name.pdf") new_filename = filename.with_suffix(".docx")from pathlib import Path filename = "mysequence.fasta" new_filename = Path(filename).stem + ".aln"