List slice assignment and custom sequences

[Erik Max Francis]

Ronald Oussoren wrote:

> No, I want to replace part of a sequence by another sequence.

If the sequence that your splicing into is a custom type, then it's
going to depend on whether such splicing is implemented and how. 
Presumably it would want a sequence on the right-hand side of the same
type as the left-hand side.

> I don't
> understand _why_ the RHS must be a list if the LHS is one. It doesn't
> even allow a tuple, even though tuples can be used instead of lists in
> almost all code that treats the sequence as read-only.

It just sounds like common sense to me; the splicing operation should
take the same type of sequence on the right-hand side as the left. 
Since Python allows you trivial conversion from _any_ sequence to a list
with the list function/type, it seems like a non-problem to me if the
right-hand side isn't a list to start with.

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