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# Effective Python

本章节作为<\<Effective Python 编写高质量Python代码的59个有效方法>>读书笔记

## 用Pythonic方式来思考

### 第1条：确认自己所用的Python版本

```python
python --version

import sys
sys.version         # str
sys.version_info    # object
```

### 第2条：遵循 PEP 8 风格指南

PEP 8 针对Python代码格式而编订的风格指南，以便在阅读代码时可以根据这些名称看出它们在Python语言中的角色

* 函数、变量及属性应该用小写字母来拼写，各单词之间以下划线相连，如 lowercase\_underscore
* 受保护的实例属性，应该以单个下划线开头，如 \_leading\_underscore
* 私有的实例属性，应该以两个下划线开头，如 \_\_double\_leading\_underscore
* 类与异常，应该以每个单词首字母大写的形式来命名，如 CapitalizedWord
* 模块级别的常量，应该全部采用大写字母来拼写，各单词之间以下划线相连，如 ALL\_CAPS
* 类中的实例方法(instance method)，应该把首个参数命名为self，以表示该对象值
* 类方法(class method)的首个参数，应该命名为cls，以表示该类自身

文件中的那些 import 语句，总是应该使用绝对导入，可分为三部分

* 标准库
* 第三方模块
* 自用模块

### 第3条：了解 bytes、str 与 unicode 的区别

由于字符类型有区别，Python代码中经常会出现两种常见的使用情境

* 开发者需要原始8位字节值，通常以utf-8(或其他编码形式)来编码的字符
* 开发者需要操作没有特定编码形式的Unicode字符

```python
# coding:utf-8
import six
def to_unicode(s, encoding='utf-8', errors='strict'):
    if six.PY2:
        return s if isinstance(s, unicode)\
               else s.decode(encoding, errors=errors)
    else:
        return s if isinstance(s, six.string_types)\
               else s.decode(encoding, errors=errors)
​
def to_byte(s, encoding='utf-8', errors='strict'):
    if six.PY2:
        return s.encode(encoding, errors=errors)\
               if isinstance(s, unicode) else s
    else:
        return s.encode(encoding, errors=errors)\
               if isinstance(s, six.string_types) else s
```

### 第 4 条：用辅助函数来取代复杂的表达式

```python
from urllib.parse import parse_qs

my_values = parse_qs('red=5&blue=0&green=', keep_blank_values=True)
print(my_values)    # {'red': ['5'], 'blue': ['0'], 'green': ['']}

def get_first_int(values, key, default=0):
    found = values.get(key, [''])
    if found[0]:
        found = int(found[0])
    else:
        found = default
    return found

print(get_first_int(my_values, 'green'))
```

### 第 5 条：了解切割序列的办法

## 函数

### 第14条：尽量用异常来表示特殊情况，而不要返回None


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