Usage of Sys.Stdout.Flush() Method

Usage of sys.stdout.flush() method

Python's standard out is buffered (meaning that it collects some of the data "written" to standard out before it writes it to the terminal). Calling sys.stdout.flush() forces it to "flush" the buffer, meaning that it will write everything in the buffer to the terminal, even if normally it would wait before doing so.

Here's some good information about (un)buffered I/O and why it's useful:

http://en.wikipedia.org/wiki/Data_buffer

Buffered vs unbuffered IO

How can I flush the output of the print function?

In Python 3, print can take an optional flush argument:

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

In Python 2, after calling print, do:

import sys
sys.stdout.flush()

By default, print prints to sys.stdout (see the documentation for more about file objects).

Python sys.stdout.flush() doesn't seem to work

Remove the "\n" that creates a new line.

sys.stdout.write("\r{} out of {}...".format(count1, x))

What does print()'s `flush` do?

Normally output to a file or the console is buffered, with text output at least until you print a newline. The flush makes sure that any output that is buffered goes to the destination.

I do use it e.g. when I make a user prompt like Do you want to continue (Y/n):, before getting the input.

This can be simulated (on Ubuntu 12.4 using Python 2.7):

from __future__ import print_function

import sys
from time import sleep

fp = sys.stdout
print('Do you want to continue (Y/n): ', end='')
# fp.flush()
sleep(5)

If you run this, you will see that the prompt string does not show up until the sleep ends and the program exits. If you uncomment the line with flush, you will see the prompt and then have to wait 5 seconds for the program to finish

Python - sys.stdout.flush() on 2 lines in python 2.7

to go to the upper line from the current one this has to be written on the stdout \x1b[1A

CURSOR_UP_ONE = '\x1b[1A' 

to erase the contents of the line \x1b[2K has to be written on stdout.

ERASE_LINE = '\x1b[2K'

this way you could go to the upper line and overwrite the data there.

data_on_first_line = CURSOR_UP_ONE + ERASE_LINE + "abc\n"
sys.stdout.write(data_on_first_line)

data_on_second_line = "def\r"
sys.stdout.write(data_on_second_line)
sys.stdout.flush()

for more details http://www.termsys.demon.co.uk/vtansi.htm#cursor

and https://stackoverflow.com/a/12586667

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