[Python-Dev] Python program name

[Michael Foord]

On 4 May 2012, at 09:44, Vinay Sajip wrote:

> IIUC, the program name of the Python executable is set to whatever argv[0] is.
> Is there a reason for this, rather than using one of the various OS-specific
> APIs [1] for getting the name of the running executable? The reason I ask is
> that in a virtual environment (venv), the exe's path is the only thing you have
> to go on, and if you don't have that, you can't find the pyvenv.cfg file and
> hence the base Python from which the venv was created.


argv[0] is the *script* name, not the executable name - surely?

The executable path is normally available in sys.executable.

Michael


> 
> Of course argv[0] is normally set to the executable's path, but there's at least
> one test (in test_sys) where Python is spawned (via subprocess) with argv[0] set
> to "nonexistent". If run from a venv created from a source build, with no Python
> 3.3 installed, this test fails because the spawned Python can't locate the
> locale encoding, and bails.
> 
> It works when run from a source build ("./python ...") because the getpath.c
> code to find a prefix looks in the directory implied by argv[0] (in the case of
> "nonexistent" => "", i.e. the current directory) for "Modules/Setup", and also
> works from a venv if created from an installed Python 3.3 (since the value of
> sys.prefix is used as a fallback check, and that value will contain that
> Python). However, when run from a venv created from a source build, with no
> Python 3.3 installed, the error occurs.
> 
> A workaround might be one of these:
> 
> 1. Use an OS-specific API rather than argv[0] to get the executable's path for
> the processing done by getpath.c in all cases, or
> 
> 2. If the file named by argv[0] doesn't exist, then use the OS-specific API to
> find the executable's path, and try with that, or
> 
> 3. If using the current logic, no prefix is found, then use the OS-specific API
> to to find the executable's path, and try with that.
> 
> I would prefer to use option 2 and change getpath.c / getpathp.c accordingly.
> Does anyone here see problems with that approach?
> 
> Regards,
> 
> Vinay Sajip
> 
> [1] http://stackoverflow.com/a/933996
> 
> 
> 
> _______________________________________________
> Python-Dev mailing list
> Python-Dev at python.org
> http://mail.python.org/mailman/listinfo/python-dev
> Unsubscribe: http://mail.python.org/mailman/options/python-dev/fuzzyman%40voidspace.org.uk
> 


--
http://www.voidspace.org.uk/


May you do good and not evil
May you find forgiveness for yourself and forgive others
May you share freely, never taking more than you give.
-- the sqlite blessing 
http://www.sqlite.org/different.html