[Python-Dev] What about PEP 299? (original) (raw)
Nick Coghlan ncoghlan at gmail.com
Wed Mar 29 14:17:40 CEST 2006
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Guido van Rossum wrote:
On 3/28/06, Charles Cazabon <python at discworld.dyndns.org> wrote:
It might be worth instead adding an option flag to the executable that implies "from the loaded module, run main() with sys.argv as its argument(s)", so the user can get this behaviour with
python -X somemodule.py. You can do "python -x somemodule" as long as somemodule.py uses the if name=='main' convention. What does your proposal add?
FWIW, you can already (Python 2.4) do something like:
------- x.py ---------
import sys
if name == main: del sys.argv[0] # Get rid of reference to ourselves mod_name = sys.argv[0] # First arg is now module to be run mod = import(mod_name) # Run the top level module code main = mod.main # Grab the main function sys.modules["main"] = mod # Make that module the main one try: sys.argv[0] = mod.file # Try to set argv[0] properly except AttributeError: pass sys.exit(main(*sys.argv)) # Run the function
Put that in site-packages and "python -mx somemodule" will do exactly as Charles describes.
Getting it to work with a filename instead of a module name would be a bit trickier, but not a lot.
However, I think PEP 299 is mainly a holdover from C/C++/Java where the top level of a module is a play area for the compiler that the runtime never really gets to see. I know I found PEP 299 appealing when I first seriously started using Python, but the appeal faded over time as I got used to the idea of being able to have control logic at the top level of a module (to the point where the idea is now thoroughly unappealing).
PEP 299's other 'use case' (trying to run another program's main function from within the current program) seems like a recipe for disaster - far better to use the subprocess module instead (since, strangely enough, application initialisation code has this tendency to assume it has sole control of the interpreter).
Cheers, Nick.
-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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