Vader Vader - 2 months ago 8
Python Question

Interaction with Python cmd module

I have a program that uses

module and looks like this:

import cmd

class Prog(cmd.Cmd):

prompt = '>>'

def do_reverse(self, line):
print line[::-1]

def do_exit(self, line):
return True

if __name__ == '__main__':

I want to write to programs
and read from its
programmatically. I'm trying to achieve that as follows:

from subprocess import Popen, PIPE

class ShellDriver(object):
def __init__(self, process):
self.process = process
self.prompt = '>>'
self.output = ''

def read(self):
while not self.output.endswith(self.prompt):
chars =
if chars == '':
self.output += chars

result = self.output.replace('\n' + self.prompt, '')
self.output = ''
return result

def execute(self, command):
self.process.stdin.write(command + '\n')

if __name__ == '__main__':
p = Popen(['python', ''], stdin=PIPE, stdout=PIPE)
cmd = ShellDriver(p)
print cmd.execute('reverse abc')

However when I ran this code from PyCharm it works fine, but when I ran it from command line it hangs. As I understood there is a conflict between consoles (console that reader script is running from and programs console) since they are trying to use the same pipes, and this issue doesn't exist in PyCharm because it redirects I\O to its own console.

Is there a way to get this working in the system console?

I'm on Windows (cross platform solution is preferable) and Python 2.7


Finally found an answer. By default interpreter works in buffered mode sending data to stdout in chunks, in order to avoid that it should be running in unbuffered mode with -u command line argument:

p = Popen(['python', '-u', ''], stdin=PIPE, stdout=PIPE)