i'm trying communicate different python interpreter in python script. wrote object supposed store subprocess , read/write stdin, stdout, stderr.
import subprocess import fcntl import os class python: def __init__(self): self.process = subprocess.popen("python", stdin=subprocess.pipe, stdout=subprocess.pipe, stderr=subprocess.pipe) fcntl.fcntl(self.process.stdout, fcntl.f_setfl, os.o_rdonly | os.o_nonblock) fcntl.fcntl(self.process.stderr, fcntl.f_setfl, os.o_rdonly | os.o_nonblock) def read(self): stdout = self.process.stdout.read() if stdout: print("stdout:", stdout) stderr = self.process.stderr.read() if stderr: print("stderr:", stderr) def exec(self, line): self.process.stdin.write(bytes((line + "\n").encode("ascii"))) self.process.stdin.flush() in init function subprocess created , stdout, stderr set nonblocking mode. read function justs prints stdout, stderr screen , exec function writes line stdin of python , flushes it. tested using simple echo script:
while true: print(input()) i able use exec method , little time later read line passed exec method using read method.
my problem doesn't work python interpreter. tried write stdin doesn't write stdout, stderr.
well did tests, , code works expect. means correctly create python interpreter , pass commands it, , interpreter correctly executes them.
the problem output pipe may buffered (and here). if writing several kbytes, beginning part, here, nothing written pipe until python interpreter exits.
way confirm :
p = python() p.exec("print('foo')") p.exec("print('bar')") p.process.stdin.close() # force interpreter exit ... time.sleep(0.1) # wait interpreter exit ... p.read() you should stdout: b'foo\r\nbar\r\n'
as suggested j.f.sebastian in comment, straight way not bothered buffering ask interpreter not buffer anything, either -u option or pythonunbuffered environment variable :
class python: def __init__(self): self.process = subprocess.popen("python -u", stdin=subprocess.pipe, stdout=subprocess.pipe, stderr=subprocess.pipe) ... 
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