Here is a simple example as per your requirements. This example is Python 3.x (slight modifications are required for 2.x).
parent.py
import subprocess
import sys
s = "test"
p = subprocess.Popen([sys.executable, "child.py"],
stdin=subprocess.PIPE,
stdout=subprocess.PIPE)
out, _ = p.communicate(s.encode())
print(out.decode())
child.py
s = input()
s = s.upper()
print(s)
I wrote and tested this on Mac OS X. There is no platform-specific code here, so there is no reason why it won't work on Win32 also.
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