Why does this code behave differently in Python3.1 than in Python2.6?

Question

I'm very new to programming so I apologize in advance if my question is too silly.

#!/usr/bin/python2.6  
import subprocess, time  
p=subprocess.Popen(['cat'], stdin=subprocess.PIPE, stdout=subprocess.PIPE)  
for i in 'abcd':  
    p.stdin.write(str.encode(i+'\n'))  
    output=p.stdout.readline()  
    print(output)  
    time.sleep(1)

Executing this code in Python 2.6 prints letters a, b, c, d , each line of output appears after a second. This is expected behavior. But in Python 3.1 execution is blocked at line output=p.stdout.readline(). How to correct this for Python 3.1?

what exactly happens when the execution is blocked? Do you have an error you could show? — Ben
– Ben, Commented Dec 20, 2009 at 19:37
not errors, only prompts for input; this code was executed in terminal window — Geo Pop
– Geo Pop, Commented Dec 20, 2009 at 19:47
At a guess it might be differences in buffering; does something change if you add a call to p.stdin.flush after the write? — user25148
– user25148, Commented Dec 20, 2009 at 19:52
Thanks a lot, you answer my question; adding p.stdin.flush() solve my problem — Geo Pop
– Geo Pop, Commented Dec 20, 2009 at 20:00

ndim · Accepted Answer · 2009-12-20 21:24:00Z

3

Appears to be a difference in buffering. Adding a p.stdin.flush() call solved the problem. (See the comments above).

Community wiki as I deserve no credits for this answer, but some answer needs to be marked accepted.

[@Geo Pop: Please "accept" this question, as it apparently is correct.]

answered Dec 20, 2009 at 21:24

community wiki

ndim

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