PyCrypto
You cannot extract a single part like part04.rar on its own. It is just one piece of a data "container".
Parts are typically named sequentially, such as filename.part01.rar , filename.part02.rar , and so on. 5GB.part04.rar
When a file is too large for a single transfer, software like WinRAR (Windows) or The Unarchiver (macOS) can split it into a numbered sequence. You cannot extract a single part like part04