__del__: when to use it? What happens when you SystemExit/NameError wrt del? Method vs function calls.

[Veek. M]

1. What are the rules for using __del__ besides: 'don't use it'.

2. What happens when I SystemExit? __del__ and gc are not invoked when I 
SystemExit and there's a circular reference - but why? The OS is going 
to reclaim the memory anyways so why be finicky about circular 
references - why can't we go ahead and call __dell_ and run gc?

3.
import foo
def __del__(self, foo=foo):
  foo.bar()

What happens here to prevent a NameError? Apparently without the foo=foo 
a NameError can occur? But why? import foo creates a reference to the 
object anyways so it's refcount will be above 0 anyways till __del__ is 
called.


4. also, are method calls more efficient than function calls?