How to force an ImportError on development machine? (pwd module)

Question

I\'m trying to use a third-party lib (docutils) on Google App Engine and have a problem with this code (in docutils):

try:
    import pwd
    do stuff
except         


        

Answer 1

Even easier than messing with __import__ is just inserting None in the sys.modules dict:

>>> import sys
>>> sys.modules['pwd'] = None
>>> import pwd
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named pwd

Answer 2

In your testing framework, before you cause docutils to be imported, you can perform this setup task:

import __builtin__
self.savimport = __builtin__.__import__
def myimport(name, *a):
  if name=='pwd': raise ImportError
  return self.savimport(name, *a)
__builtin__.__import__ = myimport

and of course in teardown put things back to normal:

__builtin__.__import__ = self.savimport

Explanation: all import operations go through __builtin__.__import__, and you can reassign that name to have such operations use your own code (alternatives such as import hooks are better for such purposes as performing import from non-filesystem sources, but for purposes such as yours, overriding __builtin__.__import__, as you see above, affords truly simple code).