some notes on python sets

according to the doc, we have a set and frozenset built-in func in
python now.

so what's frozenset?

doc says:
Set and ImmutableSet were renamed to set and frozenset.

they don't act like str and unicode, where there's a basestring! no
baseset!!

so you must use isinstance(x, (set, frozenset)).
check it with set.mro().

PS: I got a new handful type/function:
function = type(lambda : None)
Docstring:
function(code, globals[, name[, argdefs[, closure]]])

Create a function object from a code object and a dictionary.
The optional name string overrides the name from the code object.
The optional argdefs tuple specifies the default argument values.
The optional closure tuple supplies the bindings for free variables.