Are there a way to log all python stdout and stder in a file?

Question

I'm writing a python program that will run in a container, I'm sharing a directory with this container to save all logs. But I can't redirect the output.

Are there a way inside the python code to redirect all output to file?

Python 2.7

What do you want to redirect? Can you modify the code? What exactly are you trying to achieve? Post a [MCVE](http://stackoverflow.com/help/mcve) — Vincent Savard, Feb 11 '16 at 18:42
You can replace `sys.stdout` and `sys.stderr` with any file-like object. You can also `os.dup2()` file descriptors 1 and 2 for a "stronger" redirection. — Andrea Corbellini, Feb 11 '16 at 18:43
Yes, it's my own code! But I need to test and track the logs without enter the container. — Franciscon Santos, Feb 11 '16 at 18:44

score 1 · Answer 1 · edited May 23 '17 at 12:13

1

If this is just for some development testing, this should work ok.

>>> import sys
>>> f = open("/tmp/stdout", "w")
>>> sys.stdout = f
>>> print "Hello"
>>> print "Whoa"

> cat /tmp/stdout
Hello
Whoa

You may want to periodically call sys.stdout.flush() to get more real-time output.

You could also use a wrapper like this (stolen from Disable output buffering):

class Unbuffered(object):
   def __init__(self, stream):
       self.stream = stream
   def write(self, data):
       self.stream.write(data)
       self.stream.flush()
   def __getattr__(self, attr):
       return getattr(self.stream, attr)

Then you would do

sys.stdout = Unbuffered(open("/tmp/stdout", "w"))
print "foo"
print "bar"

if you need sys.stdout back, you should be able to do

sys.stdout = sys.__stdout__

edited May 23 '17 at 12:13

Community

1
1

answered Feb 11 '16 at 18:44

sberry

128,281
18
138
165

1

Or just `print >>f, "Hello"` instead of changing `sys.stdout`. – Vincent Savard Feb 11 '16 at 18:46
@VincentSavard I was going to suggest that, but figured the OP has a bunch of print statements that they don't want to change all over the place. – sberry Feb 11 '16 at 18:48
It's possible, though in this case I'd probably suggest redirecting the output with the help of his shell, e.g. `python foo.py > log.txt`. The question could benefit from additional information. – Vincent Savard Feb 11 '16 at 18:49
I tried it, but it write all the output just after the execution, and I want to track log on the fly. – Franciscon Santos Feb 11 '16 at 18:51
@VincentSavard That is also true, but I took the statement "But I can't redirect the output." to mean the OP couldn't redirect like that. – sberry Feb 11 '16 at 18:51
To disable buffering, it's enough to pass `buffering=0` to `open()`, no need for wrappers – Andrea Corbellini Feb 11 '16 at 21:13

score 1 · Answer 2 · answered Feb 11 '16 at 18:46

1

You can give a file handle to sys.stdout and sys.stderr to redirect the output or errors to a file.

For example:

stdo=sys.stdout
# need a file handle with write mode
fhandle=open("out.txt",'w');
sys.stdout=fhandle

print "I'm the output~"
......
# reset the standard output
sys.stdout=stdo

answered Feb 11 '16 at 18:46

platinhom

139
10

#platinhom I tried it, but it write all the output just after the execution, and I want to track log on the fly. – Franciscon Santos Feb 11 '16 at 18:51

score 0 · Answer 3 · answered Feb 11 '16 at 19:01

If you want both at the same time you can do this

class OutputLogger(object):
    def __init__(self, output_file='/tmp/output_file.txt'):
        self.std = sys.stdout
        self.outfile = open(output_file, 'w')
    def write(self, message):
        self.std.write(message)
        self.outfile.write(message)
    def flush(self):
        self.outfile.flush()
        self.std.flush()

And use it like

import sys
sys.stdout = OutputLogger(path_to_file)
print 'Hello Logger'

Are there a way to log all python stdout and stder in a file?

3 Answers3