Python – Disable output buffering

bufferedpythonstdout

Is output buffering enabled by default in Python's interpreter for sys.stdout?

If the answer is positive, what are all the ways to disable it?

Suggestions so far:

  1. Use the -u command line switch
  2. Wrap sys.stdout in an object that flushes after every write
  3. Set PYTHONUNBUFFERED env var
  4. sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)

Is there any other way to set some global flag in sys/sys.stdout programmatically during execution?

Best Answer

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'
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