Book Review: Python Descriptors

Ammar Najjar · Posted on September 2, 2019

book-reviewsoftware-engineering

About the book:

• Author: Jacob Zimmerman
• ISBN (pbk): 978-1-4842-3726-7
• ISBN (electronic): 978-1-4842-3727-4
• URL: https://link.springer.com/book/10.1007%2F978-1-4842-3727-4

Summary:

This book has two parts:

• First on explaining what descriptors are, data vs non-data ones, and basic implementation of the built in classmethod, staticmethod and property descriptors.

• Second on showing how to implement your custom descriptors.

Highlights:

Chapter 4: Descriptors in the Standard Library

• The property Class

class property:
    def __init__(self, fget=None, fset=None, fdel=None):
        self.fget = fget
        self.fset = fset
        self.fdel = fdel
    def __get__(self, instance, owner):
        if instance is None:
            return self
        elif self.fget is None:
            raise AttributeError("unreadable attribute")
        else:
            return self.fget(instance)
    def __set__(self, instance, value):
        if self.fset is None:
            raise AttributeError("can't set attribute")
        else:
            self.fset(instance, value)
    def __delete__(self, instance):
        if self.fdel is None:
            raise AttributeError("can't delete attribute")
        else:
            self.fdel(instance)
    def getter(self, fget):
        return type(self)(fget, self.fset, self.fdel)
    def setter(self, fset):
        return type(self)(self.fget, fset, self.fdel)
    def deleter(self, fdel):
        return type(self)(self.fget, self.fset, fdel)

• The classmethod descriptor

class classmethod:
    def __init__(self, func):
        self.func = func
    def __get__(self, instance, owner):
        return functools.partial(self.func, owner)

• The staticmethod descriptor

class staticmethod:
    def __init__(self, func):
        self.func = func
    def __get__(self, instance, owner):
        return self.func

Opinion

Enjoyable read, especially the first part, it shows the perspective of a developer who is not involved in python’s core development. He sometimes says, ask a core developer if you wanna get the exact reasoning behind it 😄

No editor needed beside you while reading, so it works well on the bus.

Conclusion:

• Level: Advanced
• I recommend this book for python developer who like to know what is going under the hood, twinkle with the interiors functionality of python, and curious how every thing works.

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