I had thought the main difference was indenting with 2 spaces instead of 4, but this style guide says 4 spaces, too. I guess Google deliberately brought themselves in sync with the Python mainstream.

This style guide looks like a superset of PEP 8 -- where PEP 8 describes what Python code should look like, this guide goes through every Python feature and lays out exactly where a sizable group of top-notch Python hackers were willing to draw the line on maintainability vs. whipupitude for large, long-running projects.