subprocess python Popen to open java jar

Question

I am new to python subprocess and i do not understand the documentation.

I am trying to run a jar file within my python program and pipe the output back to python.

sys.stdout.write("haha")
subprocess.Popen(['java', 'myjarfile.jar'], stdin= subprocess.PIPE,
 stdout = subprocess.PIPE)
ans = raw_input("")

However, this does not seem to work

• jfs: What are you trying to do? What do you expect sys.stdout.write() and raw_input() to achieve in this case?
• Terry Jan Reedy: wording and linewrap

Answer 1

To pass b'haha' bytestring as an input to the java child process and to get its stdout as ans bytestring:

#!/usr/bin/env python3
from subprocess import check_output
ans = check_output(['java', '-jar', 'myjarfile.jar'], input=b'haha')

input parameter is supported only since Python 3.4, you could use .communicate() on older Python versions:

#!/usr/bin/env python
from subprocess import Popen, PIPE
p = Popen(['java', '-jar', 'myjarfile.jar'], stdin=PIPE, stdout=PIPE)
ans = p.communicate(b'haha')[0]
if p.returncode != 0:
 raise Error