It's just a personal thing, but I kind of miss the following possibility in Python (and likewise every other language I know):
Like 
a += 1 
is the same as
a = a + 1

I'd love to see
a .= b()
as an opportunity to express
a = a.b()

Possible usages are for example linked lists or other structures, where a class's attributes or methods are/return an object of the same type.