[ python-Bugs-973507 ] sys.stdout problems with pythonw.exe

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Bugs item #973507, was opened at 2004-06-15 16:34
Message generated for change (Comment added) made by tim_one
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=973507&group_id=5470

Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Manlio Perillo (manlioperillo)
Assigned to: Nobody/Anonymous (nobody)
Summary: sys.stdout problems with pythonw.exe

Initial Comment:
>>> sys.version
'2.3.3 (#51, Dec 18 2003, 20:22:39) [MSC v.1200 32 bit
(Intel)]'
>>> sys.platform
'win32'
>>> sys.getwindowsversion()
(5, 1, 2600, 2, '')


Hi.
I have written this script for reproducing the bug:



import sys

class teeIO:
    def __init__(self, *files):
        self.__files = files

    def write(self, str):
        for i in self.__files:
            print >> trace, 'writing on %s: %s' % (i, str)
            i.write(str)

        print >> trace, '-' * 70



def tee(*files):
    return teeIO(*files)


log = file('log.txt', 'w')
err = file('err.txt', 'w')
trace = file('trace.txt', 'w')

sys.stdout = tee(log, sys.__stdout__)
sys.stderr = tee(err, sys.__stderr__)

def write(n, width):
    sys.stdout.write('x' * width)
    if n == 1: return

    write(n - 1, width)
    
try:
    1/0
except:
    write(1, 4096)



[output from err.log]
Traceback (most recent call last):
  File "sys.py", line 36, in ?
    write(1, 4096)
  File "sys.py", line 28, in write
    sys.stdout.write('x' * width)
  File "sys.py", line 10, in write
    i.write(str)
IOError: [Errno 9] Bad file descriptor




TeeIO is needed for actually read the program output,
but I don't know if the problem is due to teeIO.

The same problem is present for stderr, as can be seen
by swapping sys.__stdout__ and sys.__stderr__.

As I can see, 4096 is the buffer size for sys.stdout/err.
The problem is the same if the data is written in
chunks, ad example: write(2, 4096/2).

The bug isn't present if I use python.exe or if I write
less than 4096 bytes.


Thanks and regards   Manlio Perillo


----------------------------------------------------------------------

>Comment By: Tim Peters (tim_one)
Date: 2004-06-15 19:09

Message:
Logged In: YES 
user_id=31435

Ya, this is well known, although it may not be documented.  
pythonw's purpose in life is *not* to create (or inherit) a 
console window (a "DOS box").  Therefore stdin, stdout, and 
stderr aren't attached to anything usable.  Microsoft's C 
runtime seems to attach them to buffers that aren't 
connected to anything, so they complain if you ever exceed 
the buffer size.

The short course is that stdin, stdout and stderr are useless 
in programs without a console window, so you shouldn't use 
them.  Or you should you install your own file-like objects, 
and make them do something useful to you.

I think it would be helpful if pythonw did something fancier 
(e.g., pop up a window containing attempted output), but 
that's in new-feature terrority, and nobody has contributed 
code for it anyway.

----------------------------------------------------------------------

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