The datastructures section of the tutorial states with respect to 
"sequence unpacking" that "there is a small bit of asymmetry here: packing 
multiple values always creates a tuple, and unpacking works for any 
sequence". This is too general, as shown by the definition of assignment 
statement target in the simple_stmts section of the reference shows: 
tuples and lists are the only kinds of sequences that can appear on the 
left-hand side of an assignment statement.