substitution __str__ method of an instance

[Diez B. Roggisch]

Christian Heimes wrote:

> netimen wrote:
>> How can I substitute __str__ method of an instance?
> 
> It's not possible. For performance and other reasons most __*__ methods
> are looked up on the type only.

Is that documented somewhere? I *know* it is that way, yet I'd like to have
place to read up on it (and point to when this question pops up)

Diez