Disable output buffering

Solution 1:

From Magnus Lycka answer on a mailing list:

You can skip buffering for a whole python process using "python -u" (or#!/usr/bin/env python -u etc) or by setting the environment variable PYTHONUNBUFFERED.

You could also replace sys.stdout with some other stream like wrapper which does a flush after every call.

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

import sys
sys.stdout = Unbuffered(sys.stdout)
print 'Hello'

Solution 2:

I would rather put my answer in How to flush output of print function? or in Python's print function that flushes the buffer when it's called?, but since they were marked as duplicates of this one (what I do not agree), I'll answer it here.

Since Python 3.3, print() supports the keyword argument "flush" (see documentation):

print('Hello World!', flush=True)

Solution 3:

# reopen stdout file descriptor with write mode
# and 0 as the buffer size (unbuffered)
import io, os, sys
try:
    # Python 3, open as binary, then wrap in a TextIOWrapper with write-through.
    sys.stdout = io.TextIOWrapper(open(sys.stdout.fileno(), 'wb', 0), write_through=True)
    # If flushing on newlines is sufficient, as of 3.7 you can instead just call:
    # sys.stdout.reconfigure(line_buffering=True)
except TypeError:
    # Python 2
    sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)

Credits: "Sebastian", somewhere on the Python mailing list.