[Python-bugs-list] [ python-Bugs-416906 ] readlines() corrupts file opened for 'a' (original) (raw)

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Fri, 12 Oct 2001 13:56:50 -0700

Bugs item #416906, was opened at 2001-04-17 18:10 You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=416906&group_id=5470

Category: None Group: None Status: Closed Resolution: Wont Fix Priority: 5 Submitted By: Nobody/Anonymous (nobody) Assigned to: Guido van Rossum (gvanrossum) Summary: readlines() corrupts file opened for 'a'

Initial Comment: Version 2.1 final release for Windows (using Idle) Windows 98 2nd edition

f=open('c:\My Documents\textfile.txt', 'a') f.write('hello file\n') f.readlines()

raises the following error - it probably should.

Traceback (most recent call last): File "<pyshell#6>", line 1, in ? f.readlines() IOError: [Errno 9] Bad file descriptor

However, the file gets a bunch of garbage appended to it. In some cases, the entire contents of the GUI window gets appended.

In Redhat 6.2 (also with Version 2.1 Final)the same code just erases the file.

Comment By: Martin D Katz, Ph.D. (drbits) Date: 2001-10-12 13:56

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Under MS Windows 2K, opening the file for 'w' and then reading (with read()) also causes this.

Comment By: Tim Peters (tim_one) Date: 2001-04-18 11:24

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Note that the problem isn't just output followed by input without an intervening positioning operation: the file was opened in append mode ("a"), not append-update mode ("a+"), so input isn't "legal" period. MS can mangle part of the file even if there is a seek() in between (but doesn't if opened in append-update mode instead).

Comment By: Guido van Rossum (gvanrossum) Date: 2001-04-18 07:00

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Writing after reading without an intervening seek() is illegal in C's stdio, but the Python file object (a thin wrapper around stdio) doesn't know how to check for this error condition. So, we have to say "then don't do this".

Possible point of light: there's discussion on writing a new I/O library for Python that avoids relying on stdio. It could fix this issue, too.

Closing the bug now.

Comment By: Tim Peters (tim_one) Date: 2001-04-18 02:39

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Back to you, Guido: you're the one fond of arguing that MS is within its rights to do anything whatsoever when the rules for C stdio are broken .

Seriously, MS won't "fix" this (they'll deny it's broken).
Same kind of thing happens in straight C under MS.

BTW, note that Anonymous did not claim it's an MS bug: two different bugs were claimed (Win98SE appends crap, RH 6.2 destroys the whole file).

I don't see a realistic choice here but to say "hmm -- tough luck, don't do that".

Comment By: Guido van Rossum (gvanrossum) Date: 2001-04-17 21:17

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Assigned to Tim, because he believes that this is a Microsoft bug.

You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=416906&group_id=5470