Is it possible to stream output from a python subprocess to a webpage in real time?

Question

Thanks in advance for any help. I am fairly new to python and even newer to html.

I have been trying the last few days to create a web page with buttons to perform tasks

Answer 1

You need to use HTTP chunked transfer encoding to stream unbuffered command line output. CherryPy's wsgiserver module has built-in support for chunked transfer encoding. WSGI applications can be either functions that return list of strings, or generators that produces strings. If you use a generator as WSGI application, CherryPy will use chunked transfer automatically.

Let's assume this is the program, of which the output will be streamed.

# slowprint.py

import sys
import time

for i in xrange(5):
    print i
    sys.stdout.flush()
    time.sleep(1)

This is our web server.

2014 Version (Older cherrpy Version)

# webserver.py

import subprocess
from cherrypy import wsgiserver


def application(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/plain')])
    proc = subprocess.Popen(['python', 'slowprint.py'], stdout=subprocess.PIPE)

    line = proc.stdout.readline()
    while line:
        yield line
        line = proc.stdout.readline()


server = wsgiserver.CherryPyWSGIServer(('0.0.0.0', 8000), application)
server.start()

2018 Version

#!/usr/bin/env python2
# webserver.py
import subprocess
import cherrypy

class Root(object):
    def index(self):
        def content():
            proc = subprocess.Popen(['python', 'slowprint.py'], stdout=subprocess.PIPE)
            line = proc.stdout.readline()
            while line:
                yield line
                line = proc.stdout.readline()
        return content()
    index.exposed = True
    index._cp_config = {'response.stream': True}

cherrypy.quickstart(Root())

Start the server with python webapp.py, then in another terminal make a request with curl, and watch output being printed line by line

curl 'http://localhost:8000'