Mysterious Python pyc file corruption problems

Brian Murray brian at
Wed May 15 22:15:05 UTC 2013

On Wed, May 15, 2013 at 04:36:56PM -0400, Barry Warsaw wrote:
> Hello Developers,
> I am trying to debug and fix a particularly vexing problem in Python that
> manifests on Ubuntu in several different ways.  I have a hypothesis about the
> problem, but there are still some mysteries and I don't know how to reproduce
> it.  I think I can fix it, but I'm sending this message (and soon, another one
> to python-dev with more technical details) in the hopes that you might have
> other ideas about how it can happen, or have a reliable way to reproduce the
> bug.
> The problem can show up in any package, but Brian has started to collect a
> number of bugs that all seem to be related (and I think Steve is going to open
> a megabug to dupe them all to).  The common way this manifests is a traceback
> on an import statement.  The actual error can be a "ValueError: bad marshal
> data (unknown type code)" such as in LP: #1010077, or an "EOFError: EOF read
> where not expected" as in LP: #1060842.  We have many more instances of both
> of these.
> Both of these exceptions come from Python's marshal code (marshal.c).  marshal
> is the low-level serialization protocol used to cache Python byte code into
> .pyc files, so both of these exception imply corrupt .pyc files, and in fact,
> the workaround is always to essentially blow away the .pyc file and re-create
> it.  (Various different techniques can be used, but they all boil down to the
> same thing.)
> Another commonality is that this bug -- so far -- has not been observed in any
> Python 3.3 code, only 3.2 and earlier, including 2.7 and 2.6.

I've found one bug where the interpreter is python3.3:

This looks to be a fresh install of Raring so the apport data seems
trustworthy.  (There are some apport issues with delayed reporting and
distribution upgrades.)  I'll be doing a full search of Launchpad bugs

Brian Murray
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