[Python-Dev] is this a bug? no environment variables (original) (raw)

Guido van Rossum guido at python.org
Mon Nov 22 17:33:57 CET 2010

On Sun, Nov 21, 2010 at 9:40 PM, Glenn Linderman <v+python at g.nevcal.com> wrote:

In reviewing my notes from my experimentations with CGIHTTPServer (Python2.6) and then http.server (Python 3.2a4), I note one behavior I haven't reported as a bug, nor do I know where to start to figure it out, other than experimentally.

The experiment: launching CGIHTTPServer without environment variables, by the simple expedient of using a batch file to unset all the existing environment variables, and then launching Python2.6 with CGIHTTPServer. So it failed early: random.py fails at line 110 (Python 2.6).

What specific traceback do you get? In my copy of the code that line says

            a = long(_hexlify(_urandom(16)), 16)

and I could just imagine that _urandom() fails for some reason to do with the environment (it is a reference to os.urandom()), which, being part of the C library code, might depend on the environment.

But you're not giving enough info to debug this.

I suppose it is possible that some environment variables are used by Python directly (but I can't seem to find a documented list of them) although I would expect that usage to be optional, with fall-back defaults when they don't exist.

That is certainly the idea, but the fallbacks may not always be nice.

Environment variables used by Python or the stdlib itself are supposed to be named PYTHON if they are Python-specific, and there's a way to disable all of these (-E). But there are other environment variables (HOME and PATH come to mind) that have a broader definition and that are used in some part of the stdlib. Plus, as I mentioned, who knows what the non-Python C library uses (well, somebody probably knows, but I don't know of a central source that we can actually trust across the many platforms where Python runs).

I suppose it is even possible that some Windows APIs might depend on some environment variables, but I expected that the registry had replaced such usage completely, by now, with the environment variables mostly being a convenience tool for batch files, or for optional, temporary alteration of particular settings.

That sounds like wishful thinking. :-)

If anyone knows of documentation listing what environment variables are required by Python on Windows, I would appreciate a pointer, searches and doc browsing having not turned it up.

I'll attempt to recreate the test situation later this week with Python 3.2a4, if no one responds, but the only debug technique I can think of is to slowly remove environment variables until I find the minimum set required to run http.server successfully for my tests with CGI files.

-- --Guido van Rossum (python.org/~guido)

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