It says not to use == to check for "none-ness". It's better to use:
if variable is none:
Why? "And the reason for choosing
egg is Noneover
egg == None: The latter can be overloaded, and is likely to break when comparing valid object with None (depends on how it's implemented, but you don't expect everyone to take comparisions with None into account, do you?), while
isalways works the same."