How to continuously read from stdin (not just once input file is done)?

Question

I have these two scripts:

clock.py

#!/usr/bin/env python3
import time

while True: 
    print("True", flush=True)
    time.sleep(1)

continuous_wc.py

#!/usr/bin/env python3
import sys

def main():
    count = 0
    for line in sys.stdin:
        sys.stdout.write(str(count))
        count += 1

if __name__=='__main__':
    main()

And I run them like so:

./clock.py | ./continuous_wc.py

I'm hoping that it prints:

1
2
3
4
5
...

Every second is like a clock, because it's counting the lines in the file basically. But it doesn't output anything. Why not?

Answer 1

In addition to print(x, flush=True) you must also flush after sys.stdout.write.

Note that the programs would technically work without flush, but they would print values very infrequently, in very large chunks, as the Python IO buffer is many kilobytes. Flushing is there to make it work more real-time.

sys.stdout.write(str(count))
sys.stdout.flush()