[Python-Dev] Importing .pyc in -O mode and vice versa (original) (raw)

Josiah Carlson jcarlson at uci.edu
Mon Nov 6 17:36:14 CET 2006

Armin Rigo <arigo at tunes.org> wrote:

Hi Martin, On Sat, Nov 04, 2006 at 04:47:37PM +0100, "Martin v. L?wis" wrote: > Patch #1346572 proposes to also search for .pyc when OptimizeFlag > is set, and for .pyo when it is not set. The author argues this is > for consistency, as the zipimporter already does that.

My strong opinion on the matter is that importing a .pyc file if the .py file is not present is wrong in the first place. It caused many headaches in several projects I worked on. Typical example: someone in the project removes a .py file, and checks in this change; someone else does an 'svn up', which kills the .py in his working copy, but not the .pyc. These stale .pyc's cause pain, e.g. by shadowing the real module (further down sys.path), or simply by preventing the project's developers from realizing that they forgot to fix some imports. We regularly had obscure problems that went away as soon as we deleted all .pyc files around, but I cannot comment more on that because we never really investigated.

I had a very similar problem the other week when mucking about with a patch to ntpath . I had it in a somewhat small temporary projects folder and needed to run another project. It picked up the local ntpath.py when importing path.py, but then failed because I was working on a 2.5 derived ntpath, but I was using 2.3 to run the other project. After renaming the local ntpath, I continued to get the error until I realized "damn pyc" and was halfway through a filsystem wide search for the problem code (10 minutes elapsed).

About the only place where I have found the need for pyc-without-py importing is for zipimports, specifically as used by py2exe and other freezing applications. I don't know if we want to add a new command line option, or a future import, or something, but I think there should be some method of warning people that an import was performed without source code.

More information about the Python-Dev mailing list