The chapter 3 review that I promised for “tomorrow” (last Saturday) was lazily postponed until today. So, let’s get to it. Tarek in this chapter continues with syntax best practices, but at this time at class level. As expected the chapter requires that you have a minimal knowledge of Python classes, so I can say it’s geared to somewhat experienced programmers, and not to newcomers. There is a short explanation on sub-classing that warms up things for the next sections.

Next is the built-in method (type?) super, which was new to me. Basically super gives you access a method or attribute of a class by calling its parent directly. This is a segue into understanding the Method Resolution Order in Python, which is understanding which class has precedence over the others. For me, I haven’t dealt with such structures before it was a good and straight explanation, especially when he explains about possible pitfalls of using super. A short list of best practices helps:

  • Multiple inheritance should be avoided:
  • super usage has to be consistent: Mixing super and classic calls is a confusing practice.
  • Don’t mix old-style and new-style classes
  • Class hierarchy has to be looked over when a parent class is called

After dealing with MRO, comes what I think is one of the best sections of the book so far, where Tarek explains about object descriptors and gives a little bit of the Python’s approach to introspection. This short section is basically all code, but it’s good to have a good best practices reference, including here properties and slots.

The last part of the chapter covers meta programming, and as Chris pointed in the comments, that’s a difficult area of Python (maybe for the ones like me that don’t have a CS formation). I would have to try the examples by hand and maybe define areas in my code where I can use it, so to take fully advantage and fully understand it.

Overall, the chapter gives a good series of topics about Python classes and I enjoyed learning a little bit more things that I couldn’t understand previously. Next we will see a review of chapter 4, that deals with PEP 8 and naming best practices.