Can't pipe input to a python program

[rivest]

BPO	1012692
Nosy	@tim-one, @loewis
Files	python_pipe_bug.txt: More details...

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/tim-one'
closed_at = <Date 2004-08-22.07:18:16.000>
created_at = <Date 2004-08-20.05:31:29.000>
labels = ['OS-windows']
title = "Can't pipe input to a python program"
updated_at = <Date 2004-08-22.07:18:16.000>
user = 'https://bugs.python.org/rivest'

bugs.python.org fields:

activity = <Date 2004-08-22.07:18:16.000>
actor = 'tim.peters'
assignee = 'tim.peters'
closed = True
closed_date = None
closer = None
components = ['Windows']
creation = <Date 2004-08-20.05:31:29.000>
creator = 'rivest'
dependencies = []
files = ['1373']
hgrepos = []
issue_num = 1012692
keywords = []
message_count = 7.0
messages = ['22145', '22146', '22147', '22148', '22149', '22150', '22151']
nosy_count = 3.0
nosy_names = ['tim.peters', 'loewis', 'rivest']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1012692'
versions = []

[rivest]

Details in attached file. Basically, I want to be
able (in Windows) to pipe input as in:
type spam.txt | eggs.py
so that eggs can read the file spam.txt. But I am
getting an Errno 9: Bad file descriptor error message.

Thanks.

    Cheers,
    Ron Rivest
    rivest@mit.edu 

[Please reply to rivest@mit.edu as well...]

[loewis]

Logged In: YES
user_id=21627

What shell is this in? I cannot reproduce this in a cmd.exe
window. However, that you report the version as "Windows 5.1
(Build 2600)" and not "Microsoft Windows XP [Version
5.1.2600]" (as ver.exe does), and that you use just ">" as
the prompt suggests you might be using a different command
interpreter.

Can you please add

print sys.stdin.fileno()

into the script? On my system, it gives "0".

[rivest]

Logged In: YES
user_id=1090045

If I print out sys.stdin.fileno(), I get -1 .
Ver.exe outputs: Microsoft Windows XP [Version 5.1.2600]
This is indeed the standard command interpreter; I set the
prompt envinronment variable to output just ">".

Thanks...

    Ron Rivest

[tim-one]

Logged In: YES
user_id=31435

I see the same on my Win XP Pro SP1 box, but I expected
to. The problem is in cmd.exe (the native XP shell), and both
MS shells (command.com and cmd.exe) have had multiple
bugs with I/O redirection forever. This somewhat confused
MS KB article describes the current state for cmd.exe
systems, in part incorrectly:

"STDIN/STDOUT Redirection May Not Work If Started from a
File Association"

http://support.microsoft.com/default.aspx?kbid=321788

It works fine if you change the "eggs.py" part of your
command line to "python eggs.py", where "python" is some
string that resolves to your Python executable, or even to
a .bat script that runs python.exe explicitly. For example, I
have a py.bat on my PATH, containing just

\python23\python.exe %1 %2 %3 %4 %5 %6 %7 %8 %9

and then

type spam.txt | py eggs.py

works fine. The point is that it doesn't work if Python gets
started via .py *association*; any other way of getting
Python started works fine.

Since this has nothing to do with Python (same thing if you
use, e.g., Perl), I'm closing this as 3rd Party, Won't Fix.

BTW, the KB article above claims the problem was fixed in XP
SP1. It does indeed appear to have been fixed for stdout
redirection, but not for stdin.

You could also use Cygwin on Windows, whose default bash
shell has sane behavior in this respect.

Martin, it's sure curious that it works for you! My ver output
is also "Microsoft Windows XP [Version 5.1.2600]". Is that
enough to distinguish Home from Pro versions? I have Pro
here. What do you have? Is yours a German flavor of XP?

I'll note that I get one more line of output than Ron reported
(the first output line, about "a nonexistent pipe"):

C:\Code\python\PCbuild>type tcap.txt | eggs.py
The process tried to write to a nonexistent pipe.
Traceback (most recent call last):
  File "C:\Code\python\PCbuild\eggs.py", line 4, in ?
    text = sys.stdin.read()
IOError: [Errno 9] Bad file descriptor

[rivest]

Logged In: YES
user_id=1090045

Thanks to tim_one!

Your analysis of the situation does seem correct, and
your proposed fix (to pipe to "python eggs.py" rather than
just to "eggs.py") works fine!

I agree that the "3rd Pary; Won't Fix" designation is
appropriate.

Thanks again!

    Cheers,
    Ronald L. Rivest

[loewis]

Logged In: YES
user_id=21627

It worked for me since I didn't reproduce Ron's actions
precisely :-(
I automatically did

type spam.txt | \python23\python.exe eggs.py

since on that system, I had deleted the .py extension, so
merely typing "eggs.py" wouldn't have worked, anyway...

[tim-one]

Logged In: YES
user_id=31435

Ah, that would explain it <wink>. It's still curious that the KB
article specifically lists the bug as being in XP Pro, but
doesn't mention XP home. Then again, there are several
inaccuracies in that article ...