Book Notes: Fluent Python 2e

Unsorted Random Notes

Method calls and interpreters

• __methods__ are only meant to be called by Python interpreters, not by you directly.
• If you need to call a __method__, it’s usually better to call the related built-in function (e.g. len, iter, str, etc.) rather than __len__() directly.
• Sometimes, the __method__ and method() built-in produces different results. For example, list.sort() sorts a list in place and returns None indicating that no new object was created, while sorted(list) creates a new list and returns it. The shuffles() built-in has the same behaviour as sorted().
• Built-in types are often optimised for performance - take advantage of them when you can.
• __repr__ and __str__ - if you implement one, pick __repr__. It represents the string representation of the object, and you should be able to recreate the object from __repr__’s output. It’s also the fallback for __str__.

Python classes and inheritance

• Python doesn’t require concrete classes to actually inherit from ABCs. E.g. any class that implements __len__ satisfies the “Sized” ABC. Some call this an “interface” in other programming languages.
• In Python, “special cases aren’t special enough to break rules.” Hence __len__ always works with len(), even though the internals may be very different (e.g. optimised at C level or with special header properties).
• By implementing special methods, your objects can behave like built-in types, enabling expressive “Pythonic” coding styles.