<s>[INST] How do I unload (reload) a Python module? I have a long-running Python server and would like to be able to upgrade a service without restarting the server. What's the best way do do this?
if foo.py has changed:
    unimport foo  <-- How do I do this?
    import foo
    myfoo = foo.Foo()

 [/INST] You can reload a module when it has already been imported by using the reload builtin function in Python 2:
import foo

while True:
    # Do some things.
    if is_changed(foo):
        foo = reload(foo)

In Python 3, reload was moved to the imp module. In 3.4, imp was deprecated in favor of importlib, and reload was added to the latter. When targeting 3 or later, either reference the appropriate module when calling reload or import it.
I think that this is what you want. Web servers like Django's development server use this so that you can see the effects of your code changes without restarting the server process itself.
To quote from the docs:

Python modulesâ code is recompiled and
  the module-level code reexecuted,
  defining a new set of objects which
  are bound to names in the moduleâs
  dictionary. The init function of
  extension modules is not called a
  second time. As with all other objects
  in Python the old objects are only
  reclaimed after their reference counts
  drop to zero. The names in the module
  namespace are updated to point to any
  new or changed objects. Other
  references to the old objects (such as
  names external to the module) are not
  rebound to refer to the new objects
  and must be updated in each namespace
  where they occur if that is desired.

As you noted in your question, you'll have to reconstruct Foo objects if the Foo class resides in the foo module.
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