pkg_resources demo script

This is a script to demonstrate the somewhat aggressive dependency-checking behavior of pkg_resources.

Start by installing pkg2, then pkg1 and pkg3 in a virtualenv. For convenience, you can use source initial_install.sh to do this part for you.

Demonstrate the normal behavior:

$ pkg1script
Used from pkg2
$ pkg3script
Used from pkg2

Now uninstall pkg2 - pkg1 declares this as an install_requires dependency but pkg3 does not. Other than that pkg1 and pkg3 are identical:

pip uninstall pkg2

Now if you try to run pkg3script it still works just fine:

$ pkg3script
Fell back to pkg1

But if you try to run pkg1script it will fail:

$ pkg1script
Traceback (most recent call last):
...
pkg_resources.DistributionNotFound: The 'pkg2' distribution was not found and is required by pkg1