python - Shell pipe working asynchronously -

i thought each processes pipe connected work asynchronously doesn't.

a.py

#!/usr/bin/env python import sys import time line in sys.stdin:     time.sleep(2)     sys.stdout.write(line.upper())     sys.stdout.flush() 

and b.py

#!/usr/bin/env python import sys line in sys.stdin:     sys.stdout.write(line.capitalize())     sys.stdout.flush() 

and test.txt

hello world python 

following code show each lines 1 one 2 seconds.

$ ./a.py < test.txt hello world python 

but following code show entirely 1 time.

$ ./a.py < test.txt | ./b.py hello world python 

it looks shell pipe working synchronously. how can asynchronously?

the problem code that, although expression...

for line in sys.stdin:     # ... 

...is treating sys.stdin iterator, doesn't seem yield values until sys.stdin hits eof, behavior of sys.stdin.readlines().

for first case, hits eof immediately, in second case, has wait a.py terminate, takes 6 seconds.

you'll have rewrite code b.py this...

#!/usr/bin/env python import sys while 1:     line = sys.stdin.readline()     if not line:         break     sys.stdout.write(line.capitalize())     sys.stdout.flush() 

...using readline() call return has whole line, rather waiting eof.

you should make similar change a.py in case want pipe input other text file.