python-2.6.2 Exception: TypeError: "'NoneType' object is not callable" in ignored

[Poor Yorick]

The following code produces an error (python-2.6.2).  Either of the following
eliminates the error:

     . assign something besides mod1 (the newly-created module) to d1

     . remove the call to shelve.open

Why is there an error produced in the first place?  What is the interaction
between d1, mod1, and shelve about?  This code runs without error in python-3.1

     $ cat test1.py
     import test2
     newmodule = test2.load()

     $ cat test2.py

     import imp
     import shelve

     def load():
             text='import test2\n'
             text += '''print('hello from test3')\n'''
             code = compile(text,'<fake>', 'exec')
             mod1 = imp.new_module('newmodule')

             newdict = mod1.__dict__
             #newdict = {}

             exec(code,newdict)
             mod1
             mode = mod1
             d1['unique'] = mod1
             #d1['unique'] = ''
             return mod1

     print('hello from test2')
     d1 = {}
     cache = shelve.open('persist')

     $ python2.6 test1.py
     hello from test2
     hello from test3
     Exception TypeError: "'NoneType' object is not callable" in  ignored
     Exception TypeError: "'NoneType' object is not callable" in  ignored

-- 
Yorick