What is the process to run sub-process with pipes that connect both input and output?

Answer

The popen2() module is used to run the sub-process but due to some difficulty in processing like creation of deadlock that keep a process blocked that wait for the output from the child and child is waiting for the input. The dead lock occurs due to the fact that parent and child doesn’t have the synchronization and both are waiting to get the processor to provide the resources to one another. Use of popen3() method allow the reading of stdout and stderr to take place where the internal buffer increases and there is no read() takes place to share the resources. popen2() take care of the deadlock by providing the methods like wait() and waitpid() that finishes a process first and when a request comes it hands over the responsibility to the process that is waiting for the resources. The program is used to show the process and run it.

import popen2
fromchild, tochild = popen2.popen2("command")
tochild.write("input\n")
tochild.flush()
output = fromchild.readline()