[Tutor] Request for code critique

[Matt Hehman]

Sorry if this shows up twice, it got bounced once.

Okay, lots of good feedback to digest.  Lloyd Kvam
sent me a complete revised program.  The highlights
were as follows:

#retrieve list of known primes
def main_shelve():
	try:
		d=shelve.open('primesfile')
		try:
			primes=d['primesfile']
		except KeyError:
			primes = [2,3,5]
			d['primesfile'] = primes
		main(primes)
	finally:
		d['primesfile'] = primes
		d.close()

#defines function for finding common factors
def Euclid(a,b):
<snip>

def main(primes):
<snip a neatened up version of the rest of my program>

if __name__ = '__main__':
        main_shelve()

The use of "try:" and "finally:" is new to me (docs?) 
The last two lines are a total mystery, as is the fact
that the program actually runs (and quite nicely) when
all I can make out is that functions have been
defined.  Why does it execute?



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