Regarding this one:

http://google-styleguide.googlecode.com/svn/trunk/pyguide.ht...

I commented about this on another post. There's a nice explanation here as to why using mutable objects as default values in function/method definitions is bad:

http://effbot.org/zone/default-values.htm

In short, it can be bad to set default arguments to mutable objects because the function keeps using the same object in each call.