The Book Link https://github.com/nickcafferry/Learning-Python-4th-Edition/blob/master/learning-python.pdf
Ch27-Ch35: More realisitic example for OOP.
Ch36: Details on Unicode and byte strings; Differences between two editions 3.0 and 2.6.
Ch37: Managed attribute tools and descriptors.
Ch38: Functions and Class operators, comprehensive examples.
Ch39: Metaclasses and compares and contrasts them with decorators.
Ch36-Ch39 are officially optional reading. They are advanced topic chapters for most programmers using simple ASCII strings.