I have a python script which gets 2 parameters from the command line, an executable and a file. After I do some computation I need to pass by stdin the result of this computation to the executable.
1) is this even possible?
2) if so, how can I do this in Python
First, you should never use os.system that's a very dangerous and bad habit.
As for your problem, using subprocess you can do the following:
from subprocess import Popen, PIPE, STDOUT #do some stuff data = do_some_computation_from_file #prepare your executable using subprocess.Popen exe = Popen(['your_executable'], stdout=PIPE, stdin=PIPE, stderr=STDOUT) #pass in the computed data to the executable and grap the result result = exe.communicate(input=data)