How to redirect stdout to both file and console wi

问题:

I want to run a python script and capture the output on a text file as well as want to show on console.

I want to specify it as a property of the python script itself. NOT to use the command echo "hello world" | tee test.txt on command prompt every time.

Within script I tried:

sys.stdout = open('log.txt','w')

But this does not show the stdout output on screen.

I have heard about logging module but I could not get luck using that module to do the job.

回答1:

You can use shell redirection while executing the python file:

python foo_bar.py > file

This will write all results being printed on stdout from the python source to file to the logfile.

Or if you want logging from within the script:

import sys

class Logger(object):
    def __init__(self):
        self.terminal = sys.stdout
        self.log = open("logfile.log", "a")

    def write(self, message):
        self.terminal.write(message)
        self.log.write(message)  

    def flush(self):
        #this flush method is needed for python 3 compatibility.
        #this handles the flush command by doing nothing.
        #you might want to specify some extra behavior here.
        pass    

sys.stdout = Logger()

Now you can use:

print "Hello"

This will write "Hello" to both stdout and the logfile

回答2:

I got the way to redirect the out put to console as well as to a text file as well simultaneously:

te = open('log.txt','w')  # File where you need to keep the logs

class Unbuffered:

   def __init__(self, stream):

       self.stream = stream

   def write(self, data):

       self.stream.write(data)
       self.stream.flush()
       te.write(data)    # Write the data of stdout here to a text file as well



sys.stdout=Unbuffered(sys.stdout)

回答3:

Use logging module to debug and follow your app

Here is how I managed to log to file and to console / stdout

import logging
logging.basicConfig(level=logging.INFO,
                    format='%(asctime)s - %(levelname)s - %(message)s',
                    filename='logs_file',
                    filemode='w')
# Until here logs only to file: 'logs_file'

# define a new Handler to log to console as well
console = logging.StreamHandler()
# optional, set the logging level
console.setLevel(logging.INFO)
# set a format which is the same for console use
formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s')
# tell the handler to use this format
console.setFormatter(formatter)
# add the handler to the root logger
logging.getLogger('').addHandler(console)

# Now, we can log to both ti file and console
logging.info('Jackdaws love my big sphinx of quartz.')
logging.info('Hello world')

read it from source: https://docs.python.org/2/howto/logging-cookbook.html

回答4:

I devised an easier solution. Just define a function that will print to file or to screen or to both of them. In the example below I allow the user to input the outputfile name as an argument but that is not mandatory:

OutputFile= args.Output_File
OF = open(OutputFile, 'w')

def printing(text):
    print text
    if args.Output_File:
        OF.write(text + "\n")

After this, all that is needed to print a line both to file and/or screen is: printing(Line_to_be_printed)

回答5:

Based on Amith Koujalgi's answer, here's a simple module you can use for logging -

transcript.py:

"""
Transcript - direct print output to a file, in addition to terminal.

Usage:
    import transcript
    transcript.start('logfile.log')
    print("inside file")
    transcript.stop()
    print("outside file")
"""

import sys

class Transcript(object):

    def __init__(self, filename):
        self.terminal = sys.stdout
        self.logfile = open(filename, "a")

    def write(self, message):
        self.terminal.write(message)
        self.logfile.write(message)

    def flush(self):
        # this flush method is needed for python 3 compatibility.
        # this handles the flush command by doing nothing.
        # you might want to specify some extra behavior here.
        pass

def start(filename):
    """Start transcript, appending print output to given filename"""
    sys.stdout = Transcript(filename)

def stop():
    """Stop transcript and return print functionality to normal"""
    sys.stdout.logfile.close()
    sys.stdout = sys.stdout.terminal

回答6:

To redirect output to a file and a terminal without modifying how your Python script is used outside, you could use pty.spawn(itself):

#!/usr/bin/env python
"""Redirect stdout to a file and a terminal inside a script."""
import os
import pty
import sys

def main():
    print('put your code here')

if __name__=="__main__":
    sentinel_option = '--dont-spawn'
    if sentinel_option not in sys.argv:
        # run itself copying output to the log file
        with open('script.log', 'wb') as log_file:
            def read(fd):
                data = os.read(fd, 1024)
                log_file.write(data)
                return data

            argv = [sys.executable] + sys.argv + [sentinel_option]
            rc = pty.spawn(argv, read)
    else:
        sys.argv.remove(sentinel_option)
        rc = main()
    sys.exit(rc)

If pty module is not available (on Windows) then you could replace it with teed_call() function that is more portable but it provides ordinary pipes instead of a pseudo-terminal -- it may change behaviour of some programs.

The advantage of pty.spawn and subprocess.Popen -based solutions over replacing sys.stdout with a file-like object is that they can capture the output at a file descriptor level e.g., if the script starts other processes that can also produce output on stdout/stderr. See my answer to the related question: Redirect stdout to a file in Python?

回答7:

from IPython.utils.io import Tee
from contextlib import closing

print('This is not in the output file.')        

with closing(Tee("outputfile.log", "w", channel="stdout")) as outputstream:
    print('This is written to the output file and the console.')
    # raise Exception('The file "outputfile.log" is closed anyway.')
print('This is not written to the output file.')   

# Output on console:
# This is not in the output file.
# This is written to the output file and the console.
# This is not written to the output file.

# Content of file outputfile.txt:
# This is written to the output file and the console.

The Tee class in IPython.utils.io does what you want, but it lacks the __enter__ and __exit__ methods needed to call it in the with-statement. Those are added by contextlib.closing.

回答8:

I tried this:

"""
Transcript - direct print output to a file, in addition to terminal.

Usage:
    import transcript
    transcript.start('logfile.log')
    print("inside file")
    transcript.stop()
    print("outside file")
"""

import sys

class Transcript(object):

    def __init__(self, filename):
        self.terminal = sys.stdout, sys.stderr
        self.logfile = open(filename, "a")

    def write(self, message):
        self.terminal.write(message)
        self.logfile.write(message)

    def flush(self):
        # this flush method is needed for python 3 compatibility.
        # this handles the flush command by doing nothing.
        # you might want to specify some extra behavior here.
        pass

def start(filename):
    """Start transcript, appending print output to given filename"""
    sys.stdout = Transcript(filename)

def stop():
    """Stop transcript and return print functionality to normal"""
    sys.stdout.logfile.close()
    sys.stdout = sys.stdout.terminal
    sys.stderr = sys.stderr.terminal

回答9:

you can redirect the output to a file by using >> python with print rint's "chevron" syntax as indicated in the docs

let see,

fp=open('test.log','a')   # take file  object reference 
print >> fp , "hello world"            #use file object with in print statement.
print >> fp , "every thing will redirect to file "
fp.close()    #close the file 

checkout the file test.log you will have the data and to print on console just use plain print statement .