Can anyone explain what the commas do, and when 'a' and 'b' are defined in this code http://dpaste.com/557932/?
It's actually one of the soln on the Project Euler problem 5 thread which I don't understand. Using it to complement my 6.00 study. Thanks!

Question

anonymous · Answer

def gcd(a, b):              
    while b != 0: 
        a, b = b, a % b     ## this is the same thing as   
                                    ## a = b
                                   ## b = a % b
                                   ## this code decided to put it on one line by separating with a ','
    return a 

def lcm(a, b): 
    return a*b/gcd(a, b) 

print reduce(lcm, range(1, 20+1))

anonymous · Answer

it's called tuple unpacking: see the bottom of this, http://docs.python.org/release/1.5.1p1/tut/tuples.html

anonymous · Answer

here is another good one: http://en.wikibooks.org/wiki/Python_Programming/Tuples#Packing_and_Unpacking

anonymous · Answer

sorry bwCA, but i don't understand where's the tuple unpacking, and how a and b get their values?

anonymous · Answer

ok bwCA, i thought about it again and know where the tuple unpacking is. i'm still trying to get by head around why it works because of the order of statements, but i should be fine. thanks again!

anonymous · Answer

a,b = c,d
Is equivalent to

a=c
b=d

anonymous · Answer

http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#swap-values