[Python-Dev] linecache problem

Thomas Heller theller at python.net
Fri Sep 30 09:17:39 CEST 2005

On several occasions I have seen tracebacks in my code pointing to PIL's
__init__.py file. That is strange, because I have installed PIL but it
is used nowhere.

Finally I traced it down to a problem in the linecache code, which tries
to be smart in up updatecache function.  When os.stat() on the filename
fails with os.error, it walks along sys.path and returns the first file
with a matching basename. This *may* make sense for toplevel modules,
but never for modules in packages.

So, if the traceback's stack contains an entry for a non-existing file
(for example because the .py file for a .pyc file is no longer present),
linecache returns absolute garbage.

Example, on my system (the \a\b\c\__init__.py file doesn't exist):

C:\>python -c "import linecache; print linecache.getlines(r'\a\b\c\__init__.py')"
['#\n', '# The Python Imaging Library.\n',
'# $Id: //modules/pil/PIL/__init__.py#2 $\n', '#\n',
'# package placeholder\n', '#\n', '# Copyright (c) 1999 by Secret Labs AB.\n',
'#\n', '# See the README file for information on usage and redistribution.\n',
'#\n', '\n', '# ;-)\n']

The bug is present in 2.3, 2.4, and current CVS.


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