why are some types immutable?

[Fredrik Lundh]

Roy Smith wrote:

> But, in a nutshell, the biggest reason for immutable types (tuples and
> strings) is that this lets they be dictionary keys.

if you think that's the biggest reason, you haven't spent enough time working
on high-performance Python code and extensions (there's a reason why some
languages adopt a "you can only assign to a variable once" approach).

</F>