Fix broken code examples

There are still leftover code examples from the Python 2 days. A search for "print " on the API page pulls up 6 examples, while "print(" only pulls up 2. There may be other less obvious breakages, possibly separate from Python 2/3 incompatibilities.

To fix this, we should identify an exhaustive list of code examples in the docs, and test them all. A better long-term solution would be incorporating doctest into our unit tests, automatically ensuring all code examples actually work, though I think this is best saved for a later issue.