Usage of sys stdout flush method

Question

What does sys stdout flush   do

User · Answer

import sys for x in range 10000       print  HAPPY  gt  gt   s  lt  lt  r    str x       sys stdout flush

User · Answer

As per my understanding  When ever we execute print statements output will be written to buffer  And we will see the output on screen when buffer get flushed cleared   By default buffer will be flushed when program exits  BUT WE CAN ALSO FLUSH THE BUFFER MANUALLY by using  sys stdout flush    statement in the program  In the below code buffer will be flushed when value of i reaches 5   You can understand by executing the below code   chiru online    cat flush py   import time import sys  for i in range 10       print i     if i    5          print  Flushing buffer          sys stdout flush       time sleep 1   for i in range 10       print i      if i    5          print  Flushing buffer          sys stdout flush     chiru online    python flush py  0 1 2 3 4 5 Flushing buffer 6 7 8 9 0 1 2 3 4 5 Flushing buffer 6 7 8 9

User · Answer

Consider the following simple Python script   import time import sys  for i in range 5       print i        sys stdout flush       time sleep 1    This is designed to print one number every second for five seconds  but if you run it as it is now  depending on your default system buffering  you may not see any output until the script completes  and then all at once you will see 0 1 2 3 4 printed to the screen   This is because the output is being buffered  and unless you flush sys stdout after each print you won t see the output immediately   Remove the comment from the sys stdout flush   line to see the difference

User · Answer

As per my understanding sys stdout flush   pushes out all the data that has been buffered to that point to a file object  While using stdout  data is stored in buffer memory  for some time or until the memory gets filled  before it gets written to terminal  Using flush   forces to empty the buffer and write to terminal even before buffer has empty space

User · Answer

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

User · Answer

You can see the differences b w these two import sys  for i in range 1 10        sys stdout write str i       sys stdout flush    for i in range 1 10        print i

[python] Usage of sys.stdout.flush() method

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