Dealing with errors in interactive subprocess running python interpreter that freeze the process

[Terry Reedy]

On 8/1/2018 4:11 PM, cseberino at gmail.com wrote:
> I can run python3 interactively in a subprocess w/ Popen but
> if I sent it text, that throws an exception, the process freezes
> instead of just printing the exception like the normal interpreter..
> why? how fix?  Here is my code below.
> 
> (I suspect when there is an exception, there is NO output to stdin so that
> the problem is the line below that tries to read from stdin never finishes.
> Maybe I need a different readline that can "survive" when there is no output and won't block?)
> 
> ....
> 
> import subprocess
>   
> interpreter = subprocess.Popen(['python3', '-i'],
>                                 stdin  = subprocess.PIPE,
>                                 stdout = subprocess.PIPE,
>                                 stderr = subprocess.PIPE)
>   
> while True:
>          exp = input(">>> ").encode() + b"\n"
>          interpreter.stdin.write(exp)
>          interpreter.stdin.flush()
>          print(interpreter.stdout.readline().strip())

subprocess is not meant for interaction through the pipes.  That is why, 
I have been told, IDLE uses a socket for interaction.  Multiprocess is 
apparently better suited for interaction without resorting to a socket.

> interpreter.stdin.close()
> interpreter.terminate()
> 


-- 
Terry Jan Reedy