I have a module that redirects console outputs to the Tkinter window, which I found here on StackOverflow. It works perfectly, however, I realized I also need to save the console output to a file. But everything I tried either doesn't work, breaks the module, or nothing happens.
EDIT: I need to modify the following module so it also SAVES THE CONSOLE OUTPUT to the .txt document. BUT preserving it's current functionality
Here is the code for the module:
# 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
#
# See the comments and doc string below.
#
# 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.
#
# Recently updated it to work in both Python 2 and Python 3.
"""
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
try:
import thread
except ModuleNotFoundError: # Python 3
import _thread as thread
import os
EXC_INFO_FILENAME = 'exc_info.txt'
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
try:
from Tkinter import BOTH, END, Frame, Text, TOP, YES
import tkFont
import Queue
except ModuleNotFoundError: # Python 3
from tkinter import BOTH, END, Frame, Text, TOP, YES
import tkinter.font as tkFont
import queue as Queue
Q_EMPTY = Queue.Empty # An exception class.
queue = Queue.Queue(1000) # FIFO
def read_stdin(app, bufsize=4096):
fd = sys.stdin.fileno() # File descriptor for os.read() calls.
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)
# Create title based on the arguments passed to the spawned script:
# argv[0]: name of this script (ignored)
# argv[1]: name of script that imported this module
# argv[2]: name of redirected stream (optional)
if len(sys.argv) < 2:
title = "Output stream from unknown source"
elif len(sys.argv) < 3:
title = "Output stream from %s" % (sys.argv[1],)
else: # Assume it's a least 3.
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 text copying 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) # Start queue polling 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().decode() # Must decode for Python 3.
if not data:
data = '[EOF]'
go = False
log_insert(END, data)
log_see(END)
except Q_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 flush(self): # no-op.
pass
def __getattr__(self, attr):
if attr == 'pipe': # Attribute doesn't exist, so create it.
# 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 any have embedded space characters.
command = '"%s" "%s" "%s" "%s"' % (sys.executable, # executable
__file__, # argv[0]
os.path.basename(sys.argv[0]), # argv[1]
self.name) # argv[2]
#
# Typical command and arg values on receiving end:
# C:\Python3\python[w].exe # executable
# C:\vols\Files\PythonLib\Stack Overflow\errorwindow3k.py # argv[0]
# errorwindow3k_test.py # argv[1]
# stderr # argv[2]
# Execute this script directly as __main__ with a stdin PIPE for sending
# output to it.
try:
# Had to also make stdout and stderr PIPEs too, to 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_FILENAME, 'wt') as info:
info.write('fatal error occurred spawning output process')
info.write('exeception info:' + msg)
traceback.print_exc(file=info)
sys.exit('fatal error occurred')
return super(OutputPipe, self).__getattribute__(attr)
def write(self, data):
with self.lock:
data = data.encode() # Must encode for Python 3.
self.pipe.write(data) # First reference to pipe attr will cause an
# OutputPipe process for the stream to be created.
# Clean-up any left-over debugging file.
try:
os.remove(EXC_INFO_FILENAME) # Delete previous file, if any.
except Exception:
pass
# Redirect standard output streams in the process that imported this module.
sys.stderr = OutputPipe('stderr')
sys.stdout = OutputPipe('stdout')
I tried inserting this code after, before, and in between the module, but it didn't work or broke the module:
import sys path = 'output.txt' sys.stdout = open(path, 'w')
I also tried to do something like this, but it didn't work either.
f = open("output.txt", "w")
f.write(sys.stdout) # or "f.write(OutputPipe('stdout')" or " 'f.write(data)' between - 'def write(self, data):' "
f.close()
try:
sys.stdout = open('file.txt', 'w')
# some working code
finally:
# close file.txt
sys.stdout.close()
sys.stdout = sys.__stdout__
Update. You can write your custom logging class to suit your needs
import sys
class Logger:
def __init__(self, filename):
self.console = sys.stdout
self.file = open(filename, 'w')
def write(self, message):
self.console.write(message)
self.file.write(message)
def flush(self):
self.console.flush()
self.file.flush()
sys.stdout = Logger('file.txt')
I managed to solve my issue by adding a few lines to the code. I'll share here the full modified module code in the unlikely case that someone stumbles upon this same issue.
# 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
#
# See the comments and doc string below.
#
# 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.
#
# Recently updated it to work in both Python 2 and Python 3.
"""
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
try:
import thread
except ModuleNotFoundError: # Python 3
import _thread as thread
import os
EXC_INFO_FILENAME = 'exc_info.txt'
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
try:
from Tkinter import BOTH, END, Frame, Text, TOP, YES
import tkFont
import Queue
except ModuleNotFoundError: # Python 3
from tkinter import BOTH, END, Frame, Text, TOP, YES
import tkinter.font as tkFont
import queue as Queue
Q_EMPTY = Queue.Empty # An exception class.
queue = Queue.Queue(1000) # FIFO
def read_stdin(app, bufsize=4096):
fd = sys.stdin.fileno() # File descriptor for os.read() calls.
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)
# Create title based on the arguments passed to the spawned script:
# argv[0]: name of this script (ignored)
# argv[1]: name of script that imported this module
# argv[2]: name of redirected stream (optional)
if len(sys.argv) < 2:
title = "Output stream from unknown source"
elif len(sys.argv) < 3:
title = "Output stream from %s" % (sys.argv[1],)
else: # Assume it's a least 3.
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 text copying 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')
# Writes the console output to file!!! :) MOD
with open("Output.txt", "a") as f:
f.write('==== Start of Output Stream ====\n\n')
self.logwidget.see(END)
self.after(200, self.start_thread) # Start queue polling 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().decode() # Must decode for Python 3.
with open("Output.txt", "a") as f: # Writes the console output to file!!! :) MOD
f.write(str(data))
if not data:
data = '[EOF]'
go = False
with open("Output.txt", "a") as f: # Writes the '[EOF]' to file!!! :) MOD
f.write(str('\n' + '============ [EOF] =============' + '\n' + '\n' + '\n'))
log_insert(END, data)
log_see(END)
except Q_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 flush(self): # no-op.
pass
def __getattr__(self, attr):
if attr == 'pipe': # Attribute doesn't exist, so create it.
# 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 any have embedded space characters.
command = '"%s" "%s" "%s" "%s"' % (sys.executable, # executable
__file__, # argv[0]
os.path.basename(sys.argv[0]), # argv[1]
self.name) # argv[2]
#
# Typical command and arg values on receiving end:
# C:\Python3\python[w].exe # executable
# C:\vols\Files\PythonLib\Stack Overflow\errorwindow3k.py # argv[0]
# errorwindow3k_test.py # argv[1]
# stderr # argv[2]
# Execute this script directly as __main__ with a stdin PIPE for sending
# output to it.
try:
# Had to also make stdout and stderr PIPEs too, to 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_FILENAME, 'wt') as info:
info.write('fatal error occurred spawning output process')
info.write('exeception info:' + msg)
traceback.print_exc(file=info)
sys.exit('fatal error occurred')
return super(OutputPipe, self).__getattribute__(attr)
def write(self, data):
with self.lock:
data = data.encode() # Must encode for Python 3.
self.pipe.write(data) # First reference to pipe attr will cause an
# OutputPipe process for the stream to be created.
# Clean-up any left-over debugging file.
try:
os.remove(EXC_INFO_FILENAME) # Delete previous file, if any.
except Exception:
pass
# Redirect standard output streams in the process that imported this module.
sys.stderr = OutputPipe('stderr')
sys.stdout = OutputPipe('stdout')
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__
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
I have this somewhat complicated command line function in Python (lets call it myFunction()), and I am working to integrate it in a graphical interface (using PySide/Qt).
The GUI is used to help select inputs, and display outputs. However, myFunction is designed to work as a stand-alone command line function, and it occasionnaly prints out the progress.
My question is: how can I intercept these print calls and display them in the GUI?
I know it would be possible to modify myFunction() to send processEvents() to the GUI, but I would then lose the ability to execute myFunction() in a terminal.
Ideally, I would like something similar to Ubuntu's graphical software updater, which has a small embeded terminal-looking widget displaying what apt-get would display were it executed in a terminal.
you could redirect stdout and restore after. for example:
import StringIO
import sys
# somewhere to store output
out = StringIO.StringIO()
# set stdout to our StringIO instance
sys.stdout = out
# print something (nothing will print)
print 'herp derp'
# restore stdout so we can really print (__stdout__ stores the original stdout)
sys.stdout = sys.__stdout__
# print the stored value from previous print
print out.getvalue()
Wrap it with a function that hijacks stdout:
def stdin2file(func, file):
def innerfunc(*args, **kwargs):
old = sys.stdout
sys.stdout = file
try:
return func(*args, **kwargs)
finally:
sys.stdout = old
return innerfunc
Then simply provide a file like object that supports write():
class GUIWriter:
def write(self, stuff):
#send stuff to GUI
MyFunction = stdin2file(MyFunction, GUIWriter())
The wrapper can be turned into a decorator too:
def redirect_stdin(file):
def stdin2file(func, file):
def innerfunc(*args, **kwargs):
old = sys.stdout
sys.stdout = file
try:
return func(*args, **kwargs)
finally:
sys.stdout = old
return innerfunc
return stdin2file
The use it when declaring MyFunction():
#redirect_stdin(GUIWriter())
def MyFunction(a, b, c, d):
# any calls to print will call the 'write' method of the GUIWriter
# do stuff
Here is a Python 3 pattern using contextmanager that both encapsulates the monkey-patch technique and also ensures that sys.stdout is restored in case of an exception.
from io import StringIO
import sys
from contextlib import contextmanager
#contextmanager
def capture_stdout():
"""
context manager encapsulating a pattern for capturing stdout writes
and restoring sys.stdout even upon exceptions
Examples:
>>> with capture_stdout() as get_value:
>>> print("here is a print")
>>> captured = get_value()
>>> print('Gotcha: ' + captured)
>>> with capture_stdout() as get_value:
>>> print("here is a print")
>>> raise Exception('oh no!')
>>> print('Does printing still work?')
"""
# Redirect sys.stdout
out = StringIO()
sys.stdout = out
# Yield a method clients can use to obtain the value
try:
yield out.getvalue
finally:
# Restore the normal stdout
sys.stdout = sys.__stdout__
All printing is done via sys.stdout, which is a ordinary file-like object: iirc, it requires a method write(str). As long as your replacement has that method, it's quite easy to drop in your hook:
import sys
class CaptureOutput:
def write(self, message):
log_message_to_textbox(message)
sys.stdout = CaptureOutput()
The actual contents of log_message_to_textbox are up to you.
As part of trying to test a legacy function's 'print to stdout' side-effect, I want to capture stdout for later replay. I use mock.
goals (fulfill as many as possible!)
stdout still prints where it normally would, but there is an additional recorder
ideally, this should be 'patched' or only occur in a context
My implementation (below) has patching that seems a bit heavy / gross. Is there a saner way to do it? cStringIO? Any better parts of mock I can use, rather that my __getattr__ hack?
class StreamCapturing(object):
def __init__(self, stream):
self.captured = []
self.stream = stream
def __getattr__(self,attr):
return getattr(self.stream,attr)
def write(self, data):
self.captured.append(data)
self.stream.write(data)
import sys
import mock
with mock.patch('sys.stdout',StreamCapturing(sys.stdout)) as ctx:
sys.stdout.write('a\n')
print 'stdout'
sys.__stdout__.write("the real one\n")
print sys.stdout.captured
sys.stdout.flush()
assert getattr(sys.stdout,'captured') is None
You don't even need to save the previous stdout python does it for you and yes use cStringIO
import sys
from cStringIO import StringIO
sys.stdout = captured = StringIO()
print "test string"
# test stuff
captured = captured.getvalue()
sys.stdout = sys.__stdout__
print "captured",captured
You do not need mock in this situation:
saved_stdout = sys.stdout
sys.stdout = StreamCapturing(saved_stdout)
print "stdout"
captured = "".join(sys.stdout.captured)
sys.stdout=saved_stdout
print "captured: ", captured