named pipe input

[max(01)*]

hi there.

i have some problems understanding following behaviour.

consider this:

....
$ cat file_input_3.pl
#!/usr/bin/perl

open MIAPIPE, "una_pipe";

while ($riga = <MIAPIPE>)
{
print STDOUT ("$riga");
}

$ cat file_input_3.py
#!/usr/bin/python

import sys

MIAPIPE = open("una_pipe" , "r")

for riga in MIAPIPE:
print riga,
....

where una_pipe is a named pipe (created with mkfifo).

when i run this on console #1:

....
$ ./file_input_3.pl
....

and this un console #2:

....
$ cat > una_pipe
aaa
bbb
ccc
....

then each line typed in console #2 appears on console #1 as soon as the
line is terminated (hit return).

BUT if i try to do the same with the python code, something different
happens: i have to type ALL the lines on console #2 and complete the cat
command (ctrl-d) before seeing the lines echoed on console #1.

i tried the -u flag but doesnt seem to work.

any help?

bye

[Eric Nieuwland]

Re: named pipe input

max(01)* wrote:[color=blue]
> $ cat file_input_3.py
> #!/usr/bin/python
>
> import sys
>
> MIAPIPE = open("una_pipe" , "r")
>
> for riga in MIAPIPE:
> print riga,
> ...
> [...]
> BUT if i try to do the same with the python code, something different
> happens: i have to type ALL the lines on console #2 and complete the
> cat
> command (ctrl-d) before seeing the lines echoed on console #1.[/color]

You could try:

for riga in MIAPIPE:
print riga # NO COMMA!
sys.stdout.flus h()

[max(01)*]

Re: named pipe input

Eric Nieuwland wrote:[color=blue]
> max(01)* wrote:
>[color=green]
>> $ cat file_input_3.py
>> #!/usr/bin/python
>>
>> import sys
>>
>> MIAPIPE = open("una_pipe" , "r")
>>
>> for riga in MIAPIPE:
>> print riga,
>> ...
>> [...]
>> BUT if i try to do the same with the python code, something different
>> happens: i have to type ALL the lines on console #2 and complete the cat
>> command (ctrl-d) before seeing the lines echoed on console #1.[/color]
>
>
> You could try:
>
> for riga in MIAPIPE:
> print riga # NO COMMA!
> sys.stdout.flus h()
>[/color]

doesn't work! :-(

[Donn Cave]

Re: named pipe input

In article <3gIRe.6091$O6. 328317@news3.ti n.it>,
"max(01)*" <max2@fisso.cas a> wrote:
[color=blue]
> i have some problems understanding following behaviour.
>
> consider this:[/color]
[color=blue]
> $ cat file_input_3.pl
> #!/usr/bin/perl
>
> open MIAPIPE, "una_pipe";
>
> while ($riga = <MIAPIPE>)[/color]
....
[color=blue]
> $ cat file_input_3.py
> #!/usr/bin/python
>
> import sys
>
> MIAPIPE = open("una_pipe" , "r")
>
> for riga in MIAPIPE:[/color]

....[color=blue]
> BUT if i try to do the same with the python code, something different
> happens: i have to type ALL the lines on console #2 and complete the cat
> command (ctrl-d) before seeing the lines echoed on console #1.[/color]


Seems to me something like this came up here
not long ago. It turns out that

for line in file:

doesn't do the same thing as Perl's

while ($line = <file>)

If you use file.readline() instead (in a loop,
of course, I think you'll get the data one line
at a time, but "in file" apparently reads the
whole file first. That's what I vaguely remember,
I don't use it myself.

Donn Cave, donn@u.washingt on.edu