How to return value from child process to parent?

Question

Python

It is necessary to launch the child script from the parent script and transfer information there, preferably using the subprocess library, then the child script must process it and return it to the parent script. How can I get it back through Pipe?
This is what the child process looks like
proc = Popen(
[sys.executable, "h.py"],
shell=True,
stdout=PIPE, stderr=PIPE
)

Answer 1

Parent

from subprocess import Popen, PIPE

process = Popen(["python", "child.py"], stdout=PIPE, stdin=PIPE, shell=True)
print(process.communicate(b"Hello!")[0].decode())
print(process.wait())

user = input()
if user == "Hello!":
    print("Hello user!")