Question

I have some packages that have soft dependencies on other packages with a fall back to a default (simple) implementation.

The problem is that this is very hard to test for using unit tests. I could set up separate virtual environments, but that is hard to manage.

Is there a package or a way to achieve the following: have

import X

work as usual, but

hide_package('X')
import X

will raise an ImportError.

I keep having bugs creep into the fall-back part of my code because it is hard to test this.

Answer 1

It looks a bit dirty, but you can override the __import__ builtin:

save_import = __builtin__.__import__
def my_import(name, *rest):
    if name=="hidden":
        raise ImportError, "Hidden package"
    return save_import(name, *rest)
__builtin__.__import__ = my_import

BTW, have you read PEP 302? It seems that you can make a more robust mechanism with import hooks.