《Effective Python》读后感摘抄

《Effective Python》是一本由Brett Slatkin著作，Addison-Wesley Professional出版的Paperback图书，本书定价：USD 39.99，页数：256，特精心收集的读后感，希望对大家能有帮助。

《Effective Python》读后感(一)：Effective Python

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《Effective Python》读后感(二)：记录下对我有用的一些技巧

Item 24: Use @classmethod polymorphism to construct object generically

可以处理如何动态构建模型的问题。

Item 25: Use `super(__class__, self).__init__()` when inheriting

Item 29: use plain attributes instead of getter and setters.

Shortingcoming of @property: can only be shared by subclasses. Use deｓｃｒｉｐｔor to enable reusable property logic.

Item 31: deｓｃｒｉｐｔor

Need to use `WeakKeyDictionary` in `weakref` to keep track of attributes of different instances. A better solution is in Item 35.

Item 32: __getattr__, __getattribute__, __setattr__

__getattr__ is called if attribute cannot be found in instance dictionary.

__getattribute__ is called everytime even when attribute can be found in instance dictionary.

Avoid infinite recursion in __getattribute__ by using methods from `super()`

Item 33: validate subclasses with metaclass

Validate code in __init__ is runned after an object of the class's type is constructed. Using metaclasses can raise errors much earlier.

Item 34: register class existence with metaclass

Class registration is a helpful pattern for building modualr python programs. Using mataclasses for class registration avoids errors by ensuring that you never miss a registration call.

Item 35: annotate class attributes with metaclass

In this way you can avoid both memory leaks and `weakref` module by metaclasses along with deｓｃｒｉｐｔors.

目前只读到前4章。第5章并发和并行目前用的不多。第6章内建模块据说还不如直接读文档。第7、8章的东西对research code没啥意义，不是写大的生产项目用不着。

《Effective Python》读后感(三)：好书，有很多其他Python书籍没有覆盖的内容

Effective Python 59 SPECIFIC WAYS TO WRITE BETTER PYTHON 这本书终于读完了。从这本书里学到不少经验，以及之前忽略的知识。书中部分内容也是库的内容（这么说有失公允，大部分属都会有抄库文档的嫌疑的，因为文档包含了最多的信息），也有很多内容基本上是常识，比如七八章合作和产品的东西。这些内容，看了书也不会，不看书实践一下不会也得会。是“纸上得来终觉浅”的东西。

下面按照目录记一下有用的东西。划掉的是垃圾，加粗或者颜色的是干货。

Chapter 1: Pythonic Thinking

Item 1: Know Which Version of Python You’re Using

Item 2: Follow the PEP 8 Style Guide

Item 3: Know the Differences Between bytes, str, and unicode

Item 4: Write Helper Functions Instead of Complex Expressions

Item 5: Know How to Slice Sequences

Item 6: Avoid Using start, end, and stride in a Single Slice

Item 7: Use List Comprehensions Instead of map and filter

Item 8: Avoid More Than Two Expressions in List Comprehensions

Item 9: Consider Generator Expressions for Large Comprehensions

Item 10: Prefer enumerate Over range

Item 11: Use zip to Process Iterators in Parallel

Item 12: Avoid else Blocks After for and while Loops

Item 13: Take Advantage of Each Block in try/except/else/finally

第一张虽然是Pythonic Thinking，却提出了很多不提倡使用的Python特性。但是我觉得书中这些条条框框没有必要必须遵守。比如6，为了可读性不要在一个切片操作上用3个数字，以及12，避免使用while-else，也是为了可读性。但是我认为，用了也不一定破坏了可读性。但是初衷是好的。我觉得只要不是写的太复杂，能保持一眼看明白或者多看一眼也能看明白，甚至看三眼也看不明白但是看看注释能看明白，也是可以的。本章中我觉得3和4非常有价值，4可以极大提高可读性。从这里我们知道不一定是非要为了重用才将代码封装成函数，为了可读性进行封装也可以。毕竟，函数的名字比注释要“优雅”的多。

Chapter 2: Functions

Item 14: Prefer Exceptions to Returning None

Item 15: Know How Closures Interact with Variable Scope

Item 16: Consider Generators Instead of Returning Lists

Item 17: Be Defensive When Iterating Over Arguments

Item 18: Reduce Visual Noise with Variable Positional Arguments

Item 19: Provide Optional Behavior with Keyword Arguments

Item 20: Use None and Docstrings to Specify Dynamic Default Arguments

Item 21: Enforce Clarity with Keyword-Only Arguments

14，15，16是干货，抛出一个有时候我们希望错误打断函数运行（如果出错之后后面的代码没有价值了的话），这样更好调试。对于调用出也可以使用try-except处理，而不是罗列一些if-else。有关闭包是一个重点知识。以及迭代器，不过这里感觉也并不是太深入。有关yield我还得多花点时间研究下。后面几条基本上是为了可维护性做的一些惯例。

Chapter 3: Classes and Inheritance

Item 22: Prefer Helper Classes Over Bookkeeping with Dictionaries and Tuples

Item 23: Accept Functions for Simple Interfaces Instead of Classes

Item 24: Use @classmethod Polymorphism to Construct Objects Generically

Item 25: Initialize Parent Classes with super

Item 26: Use Multiple Inheritance Only for Mix-in Utility Classes

Item 27: Prefer Public Attributes Over Private Ones

Item 28: Inherit from collections.abc for Custom Container Types

本章是面向对象的内容。Python很好入门，但是很多人将他当做一门面向过程的语言，项目都用函数组织。其实Python是纯正的面向对象的语言。就连函数也是一等的object。目前我们公司的项目都是以函数的形式组织的，我觉得很多地方都可以使用class，重用性会更好。

Chapter 4: Metaclasses and Attributes

Item 29: Use Plain Attributes Instead of Get and Set Methods

Item 30: Consider @property Instead of Refactoring Attributes Item 31: Use Deｓｃｒｉｐｔors for Reusable @property Methods

Item 32: Use __getattr__, __getattribute__, and __setattr__ for Lazy Attributes

Item 33: Validate Subclasses with Metaclasses

Item 34: Register Class Existence with Metaclasses

Item 35: Annotate Class Attributes with Metaclasses

这一章比较好，主要讲了Python获取属性的过程。这里的内容我觉得大多数和Python有关的书都讲不到。关于获取属性的部分我结合文档写了这篇博客。有关metaclass的部分我总结了这篇博客。都是干货。

Chapter 5: Concurrency and Parallelism

Item 36: Use subprocess to Manage Child Processes

Item 37: Use Threads for Blocking I/O, Avoid for Parallelism

Item 38: Use Lock to Prevent Data Races in Threads

Item 39: Use Queue to Coordinate Work Between Threads

Item 40: Consider Coroutines to Run Many Functions Concurrently

Item 41: Consider concurrent.futures for True Parallelism

这章涉及并行，进程、线程、协程等概念。目前用到的不太多，所以没有深入研究。这部分内容要结合操作系统的知识。以后再深入了解吧。

Chapter 6: Built-in Modules

Item 42: Define Function Decorators with functools.wraps

Item 43: Consider contextlib and with Statements for Reusable try/finally Behavior

Item 44: Make pickle Reliable with copyreg

Item 45: Use datetime Instead of time for Local Clocks

Item 46: Use Built-in Algorithms and Data Structures

Item 47: Use decimal When Precision Is Paramount

Item 48: Know Where to Find Community-Built Modules

Chapter 7: Collaboration

Item 49: Write Docstrings for Every Function, Class, and Module

Item 50: Use Packages to Organize Modules and Provide Stable APIs

Item 51: Define a Root Exception to Insulate Callers from APIs

Item 52: Know How to Break Circular Dependencies

Item 53: Use Virtual Environments for Isolated and Reproducible Dependencies

Chapter 8: Production

Item 54: Consider Module-Scoped Code to Configure Deployment Environments

Item 55: Use repr Strings for Debugging Output Item 56: Test Everything with unittest

Item 57: Consider Interactive Debugging with pdb Item 58: Profile Before Optimizing

Item 59: Use tracemalloc to Understand Memory Usage and Leaks

第六章将build-in函数，不如文档详细。甚至有点过时。

第七八章是开发经验，可以参考一下。不过没有应用的话都是纸上谈兵。

就写这些吧，下一步准备结合源代码和文档研究一下常用的函数、数据结构和库。

我的博客：https://www.kawabangga.com