How can I get a process's stdin by a process id? [closed]

Answer 1

Simply write to /proc/PID/fd/1:

import os.path
pid = os.getpid() # Replace your PID here - writing to your own process is boring
with open(os.path.join('/proc', str(pid), 'fd', '1'), 'a') as stdin:
  stdin.write('Hello there\n')