On Sep 3, 10:55 pm, Manuel Graune <manuel.gra...@koeln.de> wrote: > Hello everyone, > > the standard structure of a python-program which is taught in all of > the books I on python I read by now is simply something like: > > #!/usr/bin/python > print "Hello, world!" > ^D > > While reading about structuring a larger code-base, unit-testing, etc > I stumbled on the idiom > > #!/usr/bin/python > def main(): > print "Hello, world" > if __name__ == "__main__": > main() > ^D > > While experimenting with this I found that the second version in most > cases is *a lot* faster than the simple approach. (I tried this both > on Linux and Windows) I found this even in cases where the code con- > sists simply of something like > > j=0 > for i in xrange(1000000): > j+=i > print j > > How come the main()-idiom is not "the standard way" of writing a > python-program (like e.g. in C)? > And in addition: Can someone please explain why the first version > is so much slower? > > Regards, > > Manuel > > -- > A hundred men did the rational thing. The sum of those rational choices was > called panic. Neal Stephenson -- System of the > worldhttp://www.graune.org/GnuPG_pubkey.asc > Key fingerprint = 1E44 9CBD DEE4 9E07 5E0A 5828 5476 7E92 2DB4 3C99
I'm trying to come up with an answer for you, but I can't... The if __name__ == "__main__": idiom *is* the standard way to write python programs, but it's not there to speed up programs. It's there so that your program can be executed differently whether it is called as a runnable script from the command line, or if it is imported. When you import a module, "__name__" is equal to the name of the module, but when you execute it, it's "__name__" is "__main__" If you are importing a library, you generally don't want it to fire off a bunch of processing until you call the needed functions/methods. I also use it as a testing ground, and a sort of loose documentation for my modules. I put stuff in there that shows and tests a general use of the module, but when I actually import and use it, I definitely don't want that code to run! What are you using to test the scripts? I could be completely wrong, but I find it hard to believe that the second version is much (if any) faster than the first. Then again, I don't know much about the internals... ~Sean -- http://mail.python.org/mailman/listinfo/python-list
