6

The title to this may be confusing, but basically I want to be able to do the following:

import subprocess

subprocess.call(["python"])
subprocess.call(["import", "antigravity"])
subprocess.check_call(["print","\"This is so meta\" "])
subprocess.call(["exit()"])

Expected behavior would be that it would open up a python terminal session, then open up xkcd comic 353, print 'this is so meta' to the command line, and finally exit the python command line.

Basically, I want to be able to open a python session, and run commands in it from my python script. I also want to be able to check the output of commands I run in the script. Is this possible? and if so, what library do I need to be using? Will subprocess do this?

Improve this question
9
  • So, looks like you want your own kind of commands for the python? Am I right? Commented Mar 15, 2014 at 10:59
  • yeah, I want to be able to call my own commands in python. From a separate python script. Commented Mar 15, 2014 at 10:59
  • where and how do you want your python script?? Commented Mar 15, 2014 at 11:02
  • The python script that I want to run would be the commands listed above. I want to be able to run, and implement commands in, the "python command line" from a python script like the one I wrote in the question. Commented Mar 15, 2014 at 11:08
  • See this: stackoverflow.com/questions/22131980/… Commented Mar 15, 2014 at 11:09

3 Answers 3

Reset to default
3

Something like this...

import subprocess
proc = subprocess.Popen(
    'python',stdout=subprocess.PIPE,
    stdin=subprocess.PIPE)
proc.stdin.write('import antigravity\n')
proc.stdin.write('print "something"\n')
proc.stdin.close()
result = proc.stdout.read()
print result

So we're creating a process and telling it that input will come from stdin (like someone typing). We then write anything we like to that and read the response from stdout (what would normally be printed to the screen)

Improve this answer
Sign up to request clarification or add additional context in comments.

3 Comments

this solution suffers from buffering issue
@J.F.Sebastian Well... A) The OP was asking about input which doesn't have a buffering issue and B) there are other answers on this question which have different approaches - so I'm not entirely sure what you're proposing I should do? Change mine to mimic someone else's answer? Seems a little like point stealing...
@Basic: A) Use then communicate() if you think OPs input is fixed B) "What to do": Highlight possible issues with your solution. A simple warning with the link that explains it in more detail would be enough.
2

If you need to communicate with process you should use communicate() method instead stdin.write() otherwise you can find some no desirable effects.

Warning Use communicate() rather than .stdin.write, .stdout.read or .stderr.read to avoid deadlocks due to any of the other OS pipe buffers filling up and blocking the child process.

Source: http://docs.python.org/2/library/subprocess.html#popen-objects

from subprocess import PIPE, STDOUT, Popen

e = Popen(["/usr/local/bin/python3"], stdout = PIPE, stdin = PIPE, stderr = STDOUT, shell = False)

out, err = e.communicate(b"""
import sys
print('Interactive python version: %s' % str(sys.version))
sys.exit(4)
""")
e.wait()
print ('Exit code', e.returncode)
print ('Output', out)
Improve this answer

5 Comments

+1 for .communicate(). It is appropriate if the input doesn't depend on the output. btw, you don't need to call e.wait(); .communicate() already waits for the process to finish i.e., e.returncode is not None after it returns. For readability, you could use from subprocess import Popen, PIPE, STDOUT and use triple quotes to input the commands on multiple lines instead of \n. Also, shell=False and [] around a single argument are redundant.
@J.F. Sebastion: What if the input does depend on the output?
@DerekHalden: then .communicate() is not appropriate. And you might have buffering issues that may cause a deadlock. See Q: Why not just use a pipe (popen())?
What would you use instead?
@DerekHalden: In general, pexpect module. In your particular case, I 'd try @unutbu's answer first
2

You could also use the code module:

import code
console = code.InteractiveConsole()
console.push('import antigravity')
console.push('print "something"')

If for some reason you wish to run this in a subprocess, then you could use the multiprocessing module:

import code
import multiprocessing as mp

def work():
    console = code.InteractiveConsole()
    console.push('import antigravity')
    console.push('print "something"')

if __name__ == '__main__':    
    proc = mp.Process(target=work)
    proc.start()
    proc.join()

To redirect stdout to a variable:

import code
import sys

class MyStream(object):
    def __init__(self, target):
        self.target = target
        self.value = None
    def write(self, s):
        if s.strip():
            self.value = s

sys.stdout = stream = MyStream(sys.stdout)
console = code.InteractiveConsole(locals=locals())
console.push('import antigravity')
console.push('print "something"')
sys.__stdout__.write('output: {}\n'.format(stream.value))

prints

output: something

Note that the console's sys.stdout has been redirected to MyStream(sys.stdout). It prints nothing, but stores the last string in self.value. To print to the string you could use sys.__stdout__.write (note the underscores).

Improve this answer

1 Comment

Is there a way to use this to redirect output to variables in my code?

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.