converting base class instance to derived class instance

[François Pinard]

[Gerrit]
> [François Pinard]
> > By the way, what is a "heap type"?

> http://foldoc.doc.ic.ac.uk heap [...] 1. An area of memory [...]
> 2. A data structure [...]

Wow, Gerrit, I appreciate your effort in providing this comprehensive
answer (and am saving the reference to `foldoc', which looks useful).
My question was likely ambiguous, sorry.  Reading "heap type" in an
article written in the context of Python new-style classes, I wondered
if "heap type" did not refer to some classification of Python types
which I did not know, but should know.

> http://www.python.org/dev/doc/devel/lib/module-heapq.html

If you follow the `Theory' link from the page above, you might see that
I wrote this explanation.  The editor was kind above to push my name in
there :-). Not really that I expected it, it even surprised me.  On the
other hand, it officialises a tiny bit the fact that I much like Python!

-- 
François Pinard   http://www.iro.umontreal.ca/~pinard