Best form of iterating over a lsit of lists

[tonymcgregor]

I've done what I should probably have done in the first place; read the spec. I think I basically understand now but htere's one thing still bothering me.

There is a difference between () and [] on the LHS of an assignment but it's quite subtle.
(a) = is the same as a =
[a] = requires an iterable on the RHS (with just one value)
So (a) = 2 is valid but [a] = 2 is not.

I'm guessing this use of parenthesis is to be consistent with the rules for creating tuples and lists. In (1,2) the parentheses don't make this a tuple, the comma does. The parentheses are, actually (redundant) "ordering" parentheses as in (2 + 3). On the LHS they do the same thing.
E.G.

a,(b,) = 1, 2      #invalid
a,(b,) = 1, 2,     #invalid
a,(b,) = 1, (2,)   #OK
a,(b,) = 1, (2)    #invalid
a, b   = 1, 2,     #OK
a, b,  = 1, 2      #OK

But, what I still don't get is why allow [] on the RHS at all. a, requires and iterable on the RHS just like [a]. I.E.:

(a) = 1,  #a is a tuple.
[b] = 2,  #b is an integer
#but so is c in 
c, = 1,

I can't see a need for [] on the LHS so it seems odd to allow them. Especially given the confusion with lists and tuples.