In case you don't know, on Windows an args sequence has to be converted to a command line that's compatible with CreateProcess[AsUser]. If the executable path isn't passed separately, the system has to parse it from the command line, and in this case paths with spaces need to be quoted in double quotes. That's the extent of what the system needs to see. Parsing the rest is the responsibility of the program itself once it's running. Most follow common rules. In particular, the C runtime library parses the command line into a Unix-style argv array, and the shell32 API provides a nearly identical implementation as CommandLineToArgvW. subprocess.list2cmdline is intended for this common case. Other cases, which are rare with the exception of the CMD shell, require manually processing an args sequence into a compatible command line.