change vars in place w/loop or list comprehension

I am a python newbie, and am grappling with a fundamental concept. I
want to
modify a bunch of variables in place. Consider the following:

>>> a = 'one'
>>> b = 'two'
>>> c = 'three'
>>> list = [a, b, c]
>>> for i in range(len(list)):
.... list[i] = list[i].upper()
....
>>> [a, b, c] = list
>>> a
'ONE'

or, better:

>>> a = 'one'
>>> b = 'two'
>>> c = 'three'
>>> [a, b, c] = [s.upper() for s in [a, b, c]]
>>> a
'ONE'

Both of these accomplish what I'm after; I prefer the second for its
brevity.
But either approach requires that I spell out my list of vars-to-alter
[a, b, c] twice. This strikes me as awkward, and would be difficult
with longer lists. Any suggestions for a better way to do this?

--Ken

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