[Python-Dev] Should there be a way or API for retrieving from a code object a loader method and package file where the code comes from? (original) (raw)

Rocky Bernstein rocky at gnu.org
Tue Dec 23 12:55:40 CET 2008

Now that there is a package mechanism (are package mechanisms?) like zipimporter that bundle source code into a single file, should the notion of a "file" location should be adjusted to include the package and/or importer?

Is there a standard API or routine which can extract this information given a code object?

A use case here I am thinking of here is in a stack trace or a debugger, or a tool which wants to show in great detail information from a code object possibly via a frame. For example does this come from a zipped egg? And if so, which one?

For concreteness, here is what I did and here's what I saw. Select one of the zipimporter eggs at http://code.google.com/p/pytracer and install one of these.

I did this on GNU/Linux and Python 2.5 and I look at the co_filename of one of the methods:

import tracer tracer.dict['size'].funccode.cofilename 'build/bdist.linux-i686/egg/tracer.py'

But there is no file called "build/bdist.linux-686/egg/tracer.py" in the filesystem. Instead there is a member "tracer.py" inside /usr/lib/python2.5/site-packages/tracer-0.1.0-py2.5.egg'.

It's possible I caused this egg to get built incorrectly or that setuptools has a bug which entered that misleading information. However, shouldn't there be a standard way to untangle package location, loader and member inside the package?

As best as I can tell, PEP 302 which discussed importer hooks and suggests a standard way to get file data. But it doesn't address a standard way to get container package and/or loader information.

Also I'm not sure there is a standard print string way to show member inside a package. zipimporter may insert co_filename strings like:

/usr/lib/python2.5/site-packages/tracer-0.1.0-py2.5.egg/tracer.py

but the trouble with this is that it means file routines have to scan the path and notice say that /usr/lib/python2.5/site-packages/tracer-0.1.0-py2.5.egg is a file, not a directory. And a file stat/reading routine needs to understand what kind of packager that is in order to get tracer.py information.

(Are there any file routines in place for doing this?)

Thanks.

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