From PEP 8 section of Function and method arguments :
Always use self for the first argument to instance methods.
Always use cls for the first argument to class methods.
If a function argument's name clashes with a reserved keyword, it is generally better to append a >single trailing underscore rather than use an abbreviation or spelling corruption. Thus class_ is >better than clss. (Perhaps better is to avoid such clashes by using a synonym.)
It does not say anything about the preferred naming style. I guess it should be "lower_case_with_underscores" or "mixedCase" but I am not sure. What is preferred?