Running code on module import

[Hung Jung Lu]

"John Roth" <newsgroups at jhrothjr.com> wrote:
> Look at the built-in __import__() function, and the ihooks module.
> For what you want to do, you should be able to hook __import__
> so that you get control both before and after it.

He wants action performed *after* the main() is defined, not around
the time of import of his runmain. So, in a sense, he wants something
like a metaclass for the __main__ module.

Unfortunately:

(a) Python's modules are not classes, you can't intercept module
features with metaclasses.

(b) He wants something specified at the top module, like an "import"
statement. (If the *something* were specified at the bottom, it would
make things a bit easier.)

At the moment, I can only think on the sys.exitfunc as a proper hook.
:) It's totally esoteric/un-orthodox. But for whatever it's worth,
here is one example. Since it's totally un-orthodox, do not expect it
to run properly under all circumstances. (E.g.: it won't run from
console, it won't run inside Pythonwin, etc.) But it does run when
executed with standard shell command line.

#--- demo.py
import runmain
x=3
def main(switches, args):
    if switches['print']:
        legend = args[0]
        print legend, x

#--- runmain.py
import sys
def runmain():
    args = ['The value of %s is' % sys.argv[1]]
    switches = {'print': 1}
    sys.modules['__main__'].main(switches, args)    
sys.exitfunc = runmain

#--- command line
python demo.py x

#--- result
The value of x is 3

--------------------------------

As I have said, it's best to do as the Romans do, when in Rome. Bite
the bullet and use the "if __name__ == '__main__':" that everyone else
uses. It's really not that bad looking. Any args tweaking or switches
can be done at the import of a tweaking module. Seriously, something
like below would do.

import myparams # creates args (from sys.argv) and switches

def main():
   .... uses myparams.args and myparams.switches

if __name__ == '__main__':
    main()

Hung Jung