order to call Popen for 2 piped processes

[Skaperen]

when starting 2 processes with subprocess.Popen() and connecting then together with a pipe using the stdout=PIPE option and passing the read end to the other process stdin= option, in there any library based need to launch the 2 processes in a particular order? Linux systems don't have any and other POSIX should have none. but i wonder if subprocess might. i don't know about Windows, either.