Bugs item #1177964, was opened at 2005-04-06 13:55
Message generated for change (Comment added) made by catlee
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 7
Submitted By: Folke Lemaitre (zypher)
Assigned to: Nobody/Anonymous (nobody)
Summary: Iterator on Fileobject gives no MemoryError
Initial Comment:
The following problem has only been tested on linux.
Suppose at a certain time that your machine can
allocate a maximum of X megabytes of memory. Allocating
more than X should result in python MemoryErrors. Also
suppose you have a file containing one big line taking
more than X bytes (Large binary file for example).
In this case, if you read lines from a file through the
file objects iterator, you do NOT get the expected
MemoryError as result, but an empty list.
To reproduce, create a file twice as big as your
machines memory and disable the swap.
If you run the following code:
# import os.path
#
# def test(input):
# print "Testing %s (%sMB)"%(repr(input),
os.path.getsize(input)/(1024.0*1024.0))
# count = 0
# for line in open(input):
# count = count + 1
# print " >> Total Number of Lines: %s"%count
#
# if __name__ == "__main__":
# test('test.small')
# test('test.big')
you'll get something like:
# [EMAIL PROTECTED] devel $ python2.4 bug.py
# Testing 'test.small' (20.0MB)
# >> Total Number of Lines: 1
# Testing 'test.big' (2000.0MB)
# >> Total Number of Lines: 0
----------------------------------------------------------------------
Comment By: Chris AtLee (catlee)
Date: 2006-03-31 14:53
Message:
Logged In: YES
user_id=186532
This can be fixed by having the readahead method (used by
readahead_get_line_skip, used by file_iternext) raising a
MemoryError if it can't allocate enough room for the line.
Index: Objects/fileobject.c
===================================================================
--- Objects/fileobject.c (revision 43486)
+++ Objects/fileobject.c (working copy)
@@ -1797,7 +1797,8 @@
/* Make sure that file has a readahead buffer with at least
one byte
(unless at EOF) and no more than bufsize. Returns
negative value on
- error */
+ error. Will raise a MemoryError if bufsize bytes cannot be
+ allocated. */
static int
readahead(PyFileObject *f, int bufsize)
{
@@ -1810,6 +1811,7 @@
drop_readahead(f);
}
if ((f->f_buf = PyMem_Malloc(bufsize)) == NULL) {
+ PyErr_NoMemory();
return -1;
}
Py_BEGIN_ALLOW_THREADS
----------------------------------------------------------------------
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