`pkg_resources.require()` doesn't see wxPython

Question

I'm using Distribute's pkg_resources.require() in my project to check if prerequisites are installed on the user's machine. One of the prerequisites is wxPython. But when I try pkg_resources.require('wxPython'), I'm getting the DistributionNotFound error, even though it's definitely installed and operable on my machine.

I also tried the following bit of code in the shell:

for thing in pkg_resources.working_set:
    print(thing)

It listed a bunch of Python modules I have installed, but not wxPython. If it matters, I'm on Windows, and I installed wxPython with its Windows installer.

Why is this happening?