I am answering my own question, but because I stayed up all night figuring it out, I will hopefully save others some pain. If you are getting either of the following messages after properly installing pytidylib or utidylib, this answer may help.
Learning Python on Snow Leopard, I had installed the 32-bit version of Python 2.7 so that I could use the IDLE interpreter/editor. Stackoverflow has a great explanation why I had to do this.
When I installed utidylib, I got the following error from 'import tidy':
'OSError: Couldn't find libtidy, please make sure it is installed.'
With pytidylib, I got this error when I tried 'from tidylib import tidy_document':
'OSError: Could not load libtidy using any of these names: libtidy,libtidy.so,libtidy-0.99.so.0,cygtidy-0-99-0,tidylib,libtidy.dylib,tidy.'
If you are getting these errors, please read this answer. I hope it helps you.