How to redirect stderr in Python?

python redirect stderr
EcirH picture EcirH · Dec 24, 2009 · Viewed 62.2k times · Source

I would like to log all the output of a Python script. I tried:

import sys

log = []

class writer(object):
    def write(self, data):
        log.append(data)

sys.stdout = writer()
sys.stderr = writer()

Now, if I "print 'something' " it gets logged. But if I make for instance some syntax error, say "print 'something# ", it wont get logged - it will go into the console instead.

How do I capture also the errors from Python interpreter?

I saw a possible solution here:

http://www.velocityreviews.com/forums/showpost.php?p=1868822&postcount=3

but the second example logs into /dev/null - this is not what I want. I would like to log it into a list like my example above or StringIO or such...

Also, preferably I don't want to create a subprocess (and read its stdout and stderr in separate thread).

Answer

KingRadical picture KingRadical · Dec 24, 2009

I have a piece of software I wrote for work that captures stderr to a file like so:

import sys
sys.stderr = open('C:\\err.txt', 'w')

so it's definitely possible.

I believe your problem is that you are creating two instances of writer.

Maybe something more like:

import sys

class writer(object):
    log = []

    def write(self, data):
        self.log.append(data)

logger = writer()
sys.stdout = logger
sys.stderr = logger

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