Python, logging print statements while having them print to stdout

If you use the built in logging module you can configure your loggers with as many outputs as you need: to file, to databases, to emails, etc. However it sounds like you're mixing print for two different uses: logging (recording program flow for later inspection) and prompts. The real work will be to split out those two uses of 'print' into different functions so you get what you need in each place.

A lot of people replace python's generic sys.stdout and sys.stderr to automatically do stuff to text which is being sent to the console. The real console output always lives in sys.__stdout__ and sys.__stderr__ (so you don't need to worry about somehow 'losing' it) but if you stick any object with the same methods as a file into the variables sys.stdout and sys.stderr you can do whatever you like with the output process.

Here is a program that does what you describe:

#! /usr/bin/python3

class Tee:
    def write(self, *args, **kwargs):
        self.out1.write(*args, **kwargs)
        self.out2.write(*args, **kwargs)
    def __init__(self, out1, out2):
        self.out1 = out1
        self.out2 = out2

import sys
sys.stdout = Tee(open("/tmp/log.txt", "w"), sys.stdout)

print("hello")

You can add this to your script:

import sys
sys.stdout = open('logfile', 'w')

This will make the print statements write to logfile.

If you want the option of printing to stdout and a file, you can try this:

class Tee(object):
    def __init__(self, *files):
        self.files = files
    def write(self, obj):
        for f in self.files:
            f.write(obj)

f = open('logfile', 'w')
backup = sys.stdout
sys.stdout = Tee(sys.stdout, f)

print "hello world"  # this should appear in stdout and in file

To revert to just printing to console, just restore the "backup"

sys.stdout = backup

When trying the best answer accepted on python 3.7 I had the following exception:

    Exception ignored in: <__main__.Logger object at 0x7f04083760f0>
    AttributeError: 'Logger' object has no attribute 'flush'

I added the following function to make it work:

    def flush(self):
        pass