Develop Reference

Simplest way to interact with a Python script that is called by another program?

I have a Python script client.py that is called when I start my server.py (I cannot change this).
I want the client.py script to interact with the user, i.e., ask for input and show output, but as the client.py script has been called by the server, I cannot interact with it via console.
I'd like to know what is the simplest approach to asking for input from the client.py script, given that I cannot input to STDIN. I imagine two different approaches:
Using a GUI (like TKinter). But I would have to move all my script into a thread because the main loop of the GUI will want to be on the main thread.
Using sockets and connecting either via terminal or webpage. But this feels like an overkill.
Is there any simpler option I'm not seeing?

You can make client.py temporarily override sys.stdin and sys.stdout with the system's console device whenever it needs to input from or output to the console, and restore sys.stdin and sys.stdout afterwards. In UNIX-like systems, the console device is /dev/tty, and in Windows, it is con.
For example, with a client.py like:
import sys
original_stdin = sys.stdin
original_stdout = sys.stdout
console_device = 'con' if sys.platform.startswith('win') else '/dev/tty'
def user_print(*args, **kwargs):
sys.stdout = open(console_device, 'w')
print(*args, **kwargs)
sys.stdout = original_stdout
def user_input(prompt=''):
user_print(prompt, end='')
sys.stdin = open(console_device)
value = input('')
sys.stdin = original_stdin
return value
user_print('Server says:', input())
print(user_input('Enter something for the server: '), end='')
and a server.py like:
from subprocess import Popen, PIPE
p = Popen('python client.py', stdin=PIPE, stdout=PIPE, encoding='utf-8', shell=True)
output, _ = p.communicate('Hello client\n')
print('Client says:', output)
you can interact with server.py like:
Server says: Hello client
Enter something for the server: hi
Client says: hi
Demo: https://repl.it/#blhsing/CheeryEnchantingNasm

Save C-level stream print to file in Python 2.7

I am trying to save the terminal output of a python script to a file and print the output to the terminal. Using the logging script below I was able to successfully save the python output, but my script calls GNU Radio as a class and this output is not saved currectly. I believe the problem is that GNU Radio is compiled C code and not captured in the stdout redirect. I have tried using Eli Bendersky's script as a redirect but I am not understanding how to implement this in Python 2.7. Ideally I would be able to add this C-level redirect to the Logger class and save the GNU Radio output in the same generated log file. Thanks for the help!
import sys
class Logger(object):
def __init__(self, filename="Default.log"):
self.terminal = sys.stdout
self.log = open(filename, "a")
def write(self, message):
self.terminal.write(message)
self.log.write(message)
sys.stdout = Logger("yourlogfilename.txt")
print "Hello world !" # this is should be saved in yourlogfilename.txt

Redirect all stdout/stderr globally to logger

Background
I have a very large python application that launches command-line utilities to get pieces of data it needs. I currently just redirect the python launcher script to a log file, which gives me all of the print() output, plus the output of the command-line utilities, i.e.:
python -m launcher.py &> /root/out.log
Problem
I've since implemented a proper logger via logging, which lets me format the logging statements more precisely, lets me limit log file size, etc. I've swapped out most of my print()statements with calls to my logger. However, I have a problem: none of the output from the command-line applications is appearing in my log. It instead gets dumped to the console. Also, the programs aren't all launched the same way: some are launched via popen(), some by exec(), some by os.system(), etc.
Question
Is there a way to globally redirect all stdout/stderr text to my logging function, without having to re-write/modify the code that launches these command-line tools? I tried setting setting the following which I found in another question:
sys.stderr.write = lambda s: logger.error(s)
However it fails with "sys.stderr.write is read-only".

While this is not a full answer, it may show you a redirect to adapt to your particular case. This is how I did it a while back. Although I cannot remember why I did it this way, or what the limitation was I was trying to circumvent, the following is redirecting stdout and stderr to a class for print() statements. The class subsequently writes to screen and to file:
import os
import sys
import datetime
class DebugLogger():
def __init__(self, filename):
timestamp = datetime.datetime.strftime(datetime.datetime.utcnow(),
'%Y-%m-%d-%H-%M-%S-%f')
#build up full path to filename
logfile = os.path.join(os.path.dirname(sys.executable),
filename + timestamp)
self.terminal = sys.stdout
self.log = open(logfile, 'a')
def write(self, message):
timestamp = datetime.datetime.strftime(datetime.datetime.utcnow(),
' %Y-%m-%d-%H:%M:%S.%f')
#write to screen
self.terminal.write(message)
#write to file
self.log.write(timestamp + ' - ' + message)
self.flush()
def flush(self):
self.terminal.flush()
self.log.flush()
os.fsync(self.log.fileno())
def close(self):
self.log.close()
def main(debug = False):
if debug:
filename = 'blabla'
sys.stdout = DebugLogger(filename)
sys.stderr = sys.stdout
print('test')
if __name__ == '__main__':
main(debug = True)

import sys
import io
class MyStream(io.IOBase):
def write(self, s):
logger.error(s)
sys.stderr = MyStream()
print('This is an error', stream=sys.stderr)
This make all call to sys.stderr go to the logger.
The original one is always in sys.__stderr__

How to capture print output of another module?

I was wondering if this is possible in python:
# module1
def test():
print('hey')
# module2
import module1
module1.test() # prints to stdout
Without modifying module1 is there any way to wrap this in module2 so that I can capture the
print('hey') inside a variable? Apart from running module1 as a script?

I don't want to be responsible for modifying sys.stdout and then restoring it to its previous values. The above answers don't have any finally: clause, which can be dangerous integrating this into other important code.
https://docs.python.org/3/library/contextlib.html
import contextlib, io
f = io.StringIO()
with contextlib.redirect_stdout(f):
module1.test()
output = f.getvalue()
You probably want the variable output which is <class 'str'> with the redirected stdout.
Note: this code is lifted from the official docs with trivial modifications (but tested). Another version of this answer was already given to a mostly duplicated question here: https://stackoverflow.com/a/22434594/1092940
I leave the answer here because it is a much better solution than the others here IMO.

Yes, all you need is to redirect the stdout to a memory buffer that complies with the interface of stdout, you can do it with StringIO. This works for me in 2.7:
import sys
import cStringIO
stdout_ = sys.stdout #Keep track of the previous value.
stream = cStringIO.StringIO()
sys.stdout = stream
print "hello" # Here you can do whatever you want, import module1, call test
sys.stdout = stdout_ # restore the previous stdout.
variable = stream.getvalue() # This will get the "hello" string inside the variable

Yes, you can. You need to take control of sys.stdout. Something like this:
import sys
stdout_ = sys.stdout #Keep track of the previous value.
sys.stdout = open('myoutputfile.txt', 'w') # Something here that provides a write method.
# calls to print, ie import module1
sys.stdout = stdout_ # restore the previous stdout.

For Python 3:
# redirect sys.stdout to a buffer
import sys, io
stdout = sys.stdout
sys.stdout = io.StringIO()
# call module that calls print()
import module1
module1.test()
# get output and restore sys.stdout
output = sys.stdout.getvalue()
sys.stdout = stdout
print(output)

There's No need to use another module, just class object with write attribute, with one input, which you can save in another variable. for ecample
CLASS:
class ExClass:
def __init__(self):
self.st = ''
def write(self, o): #here o is the output that goes to stdout
self.st += str(o)
MAIN Program:
import sys
stdout_ = sys.stdout
var = ExClass()
sys.stdout = var
print("Hello") # these will not be pronted
print("Hello2") # instead will be written in var.st
sys.stdout = stdout_
print(var.st)
output will be
Hello
Hello2

Sending ftplib debug output to the logging module
Based on the approach taken by jimmy kumar ahalpara answer, I was able to capture ftplib's debug output into logging. ftplib was around before the logging module and uses print to emit debug messages.
I'd tried reassigning the print function to a logging method but I couldn't get that to work. The code below works for me.
I should think this will work with other modules as well but there would not be any granularity between different module's output as it's capturing everything sent to stdout to the same logger.
# convenience class to redirect stdout to logging
class SendToLog:
def __init__(self, logging_method):
self.logger = logging
_method
def write(self, o):
if str(o).strip(): # ignore empty lines
self.logger(str(o))
import logging
import sys
# code to initialise logging output and handlers ...
# ...
# get logger for ftplib and redirect it's print output to our log
ftp_logger = logging.getLogger('ftplib')
# note: logging's debug method is passed to the class, the instance then calls this method
sys.stdout = SendToLog(ftp_logger.debug)
# code to do stuff with ftplib ...
# remember to set ftplib's debug level > 0 or there will be no output
# FTP.set_debuglevel(1)
# ...
# important to finalise logging and restore stdout
logging.shutdown()
sys.stdout = sys.__stdout__
python3 stdout ftplib logging

Writing to easygui textbox as function is running?

I am currently running a script using easygui to receive the user input. The old script that ran in a command line would just print anything the user needed to know in the command line, but I've changed it to output notifications in new easygui boxes when there are required inputs.
Want I want to do is have the progress, each action inside the functions that are running, print into a text box as they complete. In command line I could just use print "text" but I can't get it to happen realtime in easygui. Currently I'm appending a list so I have a textbox that displays the results of the function once everything is complete, but I'd like for the large textbox window to pop up and print the line out whenever a process of note completes. Is this doable?
Here is how I'm appending the list:
result_list = []
record_str = "\n Polling has completed for 502."
result_list.append(record_str)
eg.textbox("Polling Status", "Daily polling completion status:", result_list)

I don't think there's any simple way of getting EasyGUI's textbox function to do what you want short of modifying the module. Since it's a function not a class, you can't even derive a subclass from it in order to easily reuse its code.
However it's completely feasible to create a separate Tkinter window that just displays lines of text as they are sent to it using an enhanced version of some code I found once in a thread on the comp.lang.python newsgroup.
The original code was designed to catch and display only stderr output from a GUI application which normally doesn't have stderr output handle, so the module was named errorwindow. However I modified it to be able redirect both stderr and stdout to such windows in one easygui-based app I developed, but I never got around to renaming it or updating the comments in it to also mention stdout redirection. ;¬)
Anyway, the module works by defining and creating two instances of a file-like class named OutputPipe when it's imported and assigns them to the sys.stdout and sys.stderr I/O stream file objects which are usually None in a Python .pyw GUI applications (on Windows). When output is first sent to either one of these, the same module is launched as separate Python process with its stdin, stdout, and stderr I/O handles piped with the original process.
There's a lot going on, but if nothing else, with a little study of it might give you some ideas about how to get easygui's textbox to do what you want. Hope this helps.
Note: The code posted is for Python 2.x, there's a modified version that will work in both Python 2 and 3 in my answer to another question, if anyone is interested.
File errorwindow.py:
# Code derived from Bryan Olson's source posted in this related Usenet discussion:
# https://groups.google.com/d/msg/comp.lang.python/HWPhLhXKUos/TpFeWxEE9nsJ
# https://groups.google.com/d/msg/comp.lang.python/HWPhLhXKUos/eEHYAl4dH9YJ
#
# Here's a module to show stderr output from console-less Python
# apps, and stay out of the way otherwise. I plan to make a ASPN
# recipe of it, but I thought I'd run it by this group first.
#
# To use it, import the module. That's it. Upon import it will
# assign sys.stderr.
#
# In the normal case, your code is perfect so nothing ever gets
# written to stderr, and the module won't do much of anything.
# Upon the first write to stderr, if any, the module will launch a
# new process, and that process will show the stderr output in a
# window. The window will live until dismissed; I hate, hate, hate
# those vanishing-consoles-with-critical-information.
#
# The code shows some arguably-cool tricks. To fit everthing in
# one file, the module runs the Python interpreter on itself; it
# uses the "if __name__ == '__main__'" idiom to behave radically
# differently upon import versus direct execution. It uses TkInter
# for the window, but that's in a new process; it does not import
# TkInter into your application.
#
# To try it out, save it to a file -- I call it "errorwindow.py" -
# - and import it into some subsequently-incorrect code. For
# example:
#
# import errorwindow
#
# a = 3 + 1 + nonesuchdefined
#
# should cause a window to appear, showing the traceback of a
# Python NameError.
#
# --
# --Bryan
# ----------------------------------------------------------------
#
# martineau - Modified to use subprocess.Popen instead of the os.popen
# which has been deprecated since Py 2.6. Changed so it
# redirects both stdout and stderr. Added numerous
# comments, and also inserted double quotes around paths
# in case they have embedded space characters in them, as
# they did on my Windows system.
"""
Import this module into graphical Python apps to provide a
sys.stderr. No functions to call, just import it. It uses
only facilities in the Python standard distribution.
If nothing is ever written to stderr, then the module just
sits there and stays out of your face. Upon write to stderr,
it launches a new process, piping it error stream. The new
process throws up a window showing the error messages.
"""
import subprocess
import sys
import thread
import os
if __name__ == '__main__': # when spawned as separate process
# create window in which to display output
# then copy stdin to the window until EOF
# will happen when output is sent to each OutputPipe created
from Tkinter import BOTH, END, Frame, Text, TOP, YES
import tkFont
import Queue
queue = Queue.Queue(100)
def read_stdin(app, bufsize=4096):
fd = sys.stdin.fileno() # gets file descriptor
read = os.read
put = queue.put
while True:
put(read(fd, bufsize))
class Application(Frame):
def __init__(self, master=None, font_size=8, text_color='#0000AA', rows=25, cols=100):
Frame.__init__(self, master)
# argv[0]: name of this script (not used)
# argv[1]: name of script that imported this module
# argv[2]: name of redirected stream (optional)
if len(sys.argv) < 3:
title = "Output Stream from %s" % (sys.argv[1],)
else:
title = "Output Stream '%s' from %s" % (sys.argv[2], sys.argv[1])
self.master.title(title)
self.pack(fill=BOTH, expand=YES)
font = tkFont.Font(family='Courier', size=font_size)
width = font.measure(' '*(cols+1))
height = font.metrics('linespace')*(rows+1)
self.configure(width=width, height=height)
self.pack_propagate(0) # force frame to be configured size
self.logwidget = Text(self, font=font)
self.logwidget.pack(side=TOP, fill=BOTH, expand=YES)
# Disallow key entry, but allow copy with <Control-c>
self.logwidget.bind('<Key>', lambda x: 'break')
self.logwidget.bind('<Control-c>', lambda x: None)
self.logwidget.configure(foreground=text_color)
#self.logwidget.insert(END, '==== Start of Output Stream ====\n\n')
#self.logwidget.see(END)
self.after(200, self.start_thread, ())
def start_thread(self, _):
thread.start_new_thread(read_stdin, (self,))
self.after(200, self.check_q, ())
def check_q(self, _):
log = self.logwidget
log_insert = log.insert
log_see = log.see
queue_get_nowait = queue.get_nowait
go = True
while go:
try:
data = queue_get_nowait()
if not data:
data = '[EOF]'
go = False
log_insert(END, data)
log_see(END)
except Queue.Empty:
self.after(200, self.check_q, ())
go = False
app = Application()
app.mainloop()
else: # when module is first imported
import traceback
class OutputPipe(object):
def __init__(self, name=''):
self.lock = thread.allocate_lock()
self.name = name
def __getattr__(self, attr):
if attr == 'pipe': # pipe attribute hasn't been created yet
# launch this module as a separate process to display any output
# it receives.
# Note: It's important to put double quotes around everything in case
# they have embedded space characters.
command = '"%s" "%s" "%s" "%s"' % (sys.executable, # command
__file__, # argv[0]
os.path.basename(sys.argv[0]), # argv[1]
self.name) # argv[2]
# sample command and arg values on receiving end:
# E:\Program Files\Python\python[w].exe # command
# H:\PythonLib\TestScripts\PyRemindWrk\errorwindow.py # argv[0]
# errorwindow.py # argv[1]
# stderr # argv[2]
# execute this script as __main__ with a stdin PIPE for sending output to it
try:
# had to make stdout and stderr PIPEs too, to make it work with pythonw.exe
self.pipe = subprocess.Popen(command, bufsize=0,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE).stdin
except Exception:
# output exception info to a file since this module isn't working
exc_type, exc_value, exc_traceback = sys.exc_info()
msg = ('%r exception in %s\n' %
(exc_type.__name__, os.path.basename(__file__)))
with open('exc_info.txt', 'wt') as info:
info.write('msg:' + msg)
traceback.print_exc(file=info)
sys.exit('fatal error occurred spawning output process')
return super(OutputPipe, self).__getattribute__(attr)
def write(self, data):
with self.lock:
self.pipe.write(data) # 1st reference to pipe attr will cause it to be created
# redirect standard output streams in the process importing the module
sys.stderr = OutputPipe('stderr')
sys.stdout = OutputPipe('stdout')