[Python-Dev] towards a stricter definition of sys.executable (original) (raw)

Thomas Heller theller at python.net
Thu Mar 16 17:35:11 CET 2006

Fredrik Lundh wrote:

the definition of sys.executable is a bit unclear, something that has led to incompatible use in deployed code.

the docstring for sys.executable says "pathname of this Python interpreter", which can be interpreted as either a) sys.executable points to the executable that was used to load the Python interpreter library/dll. this use is supported by the docstring and the implementation, and is quite common in the wild. an application using this interpretation may - call sys.executable to run another instance of itself - extract data from resources embedded in (or attached to) sys.executable - locate configuration data etc via os.path.dirname(sys.executable) etc. or b) sys.executable points to a standard Python interpreter executable of the same version, and having the same library, as the currently running interpreter instance. this use is supported by more strict interpretation of the word "interpreter" (as an executable, rather than an implementation DLL), and is quite common in the wild. an application using this interpretation may - call sys.executable to run a Python script in the same environment as itself. etc. or c) sys.executable points to the file containing the actual ("this") interpreter. I haven't seen any code that assumes this, probably because no implementation uses this interpretation... for programs that are invoked via the standard interpreter, case (a) and (b) are of course identical.

py2exe used the a) interpretation. It uses sys.executable to find the exe that is currently running, for registration of COM servers, and for finding resources in the exe: the manifest file that's needed for GUI applications on WindowsXP to give the native XP look and feel, icons, typelibs, and more.

the problem is when the interpreter library is embedded in some other application; should sys.executable be set to the actual EXE used to start the program, or to something else ? if it's set to something else, how can that application do the things that's described under (a) ?

The use case for b) 'call sys.executable to run a Python script' makes no sense for a py2exe'd application.

Thomas

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