Think about: module v function v class...

* can you effectively have portable functions?

def foo(...):
    import shlex # ...

-or-

@requires(shlex)
def foo(...):
    # ...

Idea: package from2to:
- module2package
- package2module  # not always possible
- function2module # requires import knowledge

Issues:
- what about a function that has its own exception type? e.g.::

  def edit():
    class EditException(Exception):
      """exceptions when editing"""

  Stick in globals()?  You need to expose such that the exception can
  be caught (or there's no purpose in doing this).

Links:
- http://wheel.readthedocs.org/en/latest/