Bugs item #1174606, was opened at 2005-04-01 04:48
Message generated for change (Comment added) made by jafo
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Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Adam Olsen (rhamphoryncus)
Assigned to: Nobody/Anonymous (nobody)
Summary: Reading /dev/zero causes SystemError
Initial Comment:
$ python -c 'open("/dev/zero").read()'
Traceback (most recent call last):
File "<string>", line 1, in ?
SystemError: ../Objects/stringobject.c:3316: bad
argument to internal function
Compare with this two variants:
$ python -c 'open("/dev/zero").read(2**31-1)'
Traceback (most recent call last):
File "<string>", line 1, in ?
MemoryError
$ python -c 'open("/dev/zero").read(2**31)'
Traceback (most recent call last):
File "<string>", line 1, in ?
OverflowError: long int too large to convert to int
The unsized read should produce either MemoryError or
OverflowError instead of SystemError.
Tested with Python 2.2, 2.3, and 2.4.
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>Comment By: Sean Reifschneider (jafo)
Date: 2005-04-06 03:39
Message:
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I am able to reproduce this on a Fedora Core 3 Linux system:
>>> fp = open('/dev/zero', 'rb')
>>> d = fp.read()
Traceback (most recent call last):
File "<stdin>", line 1, in ?
MemoryError
>>> print os.stat('/dev/zero').st_size
0
What about only trusting st_size if the file is a regular
file, not a directory or other type of special file?
Sean
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Comment By: Armin Rigo (arigo)
Date: 2005-04-02 12:31
Message:
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os.stat() doesn't always give consistent results on dev files. On my machine
for some reason os.stat('/dev/null') appears to be random (and extremely
large). I suspect that on the OP's machine os.stat('/dev/zero') is not 0
either, but a random number that turns out to be negative, hence a "bad
argument" SystemError.
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Comment By: Martin v. Löwis (loewis)
Date: 2005-04-01 21:42
Message:
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I think it should trust the stat result, and then find that
it cannot allocate that much memory.
Actually, os.stat("/dev/zero").st_size is 0, so something
else must be going on.
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Comment By: Armin Rigo (arigo)
Date: 2005-04-01 09:58
Message:
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I think that file.read() with no argument needs to be more conservative.
Currently it asks and trusts the stat() to get the file size, but this can lead
to just plain wrong results on special devices. (I had the problem that
open('/dev/null').read() would give a MemoryError!)
We can argue whether plain read() on special devices is a good idea or not, but
I guess that not blindly trusting stat() if it returns huge values could be a
good idea.
----------------------------------------------------------------------
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