How to I restart an interactive session?

[markscottwright]

But, by deleting their namespace entries haven't I effectively unloaded
them?  In other words, from the point of the interpreter, isn't the
state at point A and point B the same?

    --- point A:
      import os
      del __main__.__dict__['os']
    --- point B

I guess my question boils down to, is the state of the python
interpreter kept anywhere other than the __main__ namespace?  Obviously
the answer is yes - there's the current working directory and any
running threads.  I think I'm willing to live with those (yeah, I know,
those are the words of a man who is going to spend time chasing obscure
side-effects...)

But are there other things I'm missing?  Is my whole plan misguided
from the beginning?