Is there a particular reason to? If we're not trying to prevent a circular import and we're not protecting against an environment where they might not be installed, it just ends up being harder to find all the dependencies when learning from this as a sample.

I didn't realize this but PEP8 actually states:
"Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants."
http://www.python.org/dev/peps/pep-0008/

so if we don't have to do otherwise, we should always have imports at the top.