[ python-Bugs-1488717 ] appended file on Windows reads arbitrary data

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Mon May 15 18:58:26 CEST 2006


Bugs item #1488717, was opened at 2006-05-15 05:08
Message generated for change (Comment added) made by tim_one
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Category: Python Library
>Group: Not a Bug
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: muimi (muimi)
Assigned to: Nobody/Anonymous (nobody)
Summary: appended file on Windows reads arbitrary data

Initial Comment:
checked with versions 2.3 & 2.4.2 on Windows 2000 & XP

reading an appended file without resetting its
current position causes reading/writing of arbitrary data.
this appears to be related to the MS Visual Studio C
library.

def bug(filename):
    af=open(filename,'a+')
    af.write('\nlast line?')
    print af.tell()
    d=af.read() # this causes a read/write problem
    print len(d), af.tell()
    af.close()

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>Comment By: Tim Peters (tim_one)
Date: 2006-05-15 12:58

Message:
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user_id=31435

Yes, and this is inherited from the platform C library,
which conforms to the C standard in this respect:  all
behavior is undefined if you read after write, or write
after read, without a file-positioning operation (typically
a seek) between them.  So don't do that.  Closing as not-a-bug.

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

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