Python carriage return and thread

Question

So I have a script that will continuously read from a sensor, print a carriage return and then the sensor value. It does this until raw_input() finishes blocking (enter pressed).

However, when I run it, instead of an increasing number, I see blank space. When I press enter, one number is printed and then the program exits. If \\r is replaced by \\n , the program runs as it should, printing out the "sensor" value ( i = i + 1 is a placeholder for the reading of the sensor), but instead of reusing the same line it prints it on a new line. Why does it not work with \\r ? Here is the full code:

from threading import Thread
from time import sleep
import sys

running = True

def loop():
        i = 0
        while running:
                sys.stdout.write("\r" + str(i))
                i = i+1
                sleep(0.1)


thread = Thread(target=loop)
thread.start()
raw_input()
running = False
thread.join()

Answer 1

The difference is that writing out the newline flushes the channel, while writing out a carriage return (or most other character) doesn't. You can get the same behaviour by adding an explicit flush after the write():

sys.stdout.flush()

As to why the lack of a flush causes the raw_input() to never return, I believe this is due to the buffering present on stdout; however, I've not been able to find more details.

Answer 2

I was trying things and tried flushing the output with sys.stdout.flush() and it worked. Thank you all for your help.