Usage of main()

[Manuel Graune]

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 world
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