style.md

# 代码规范(风格)

一个正式的项目一般都有对应的代码规范，代码规范约定了如何在项目中编写代码。一般来说，个人开发可以使用任何自己喜欢的代码规范，但是在团队开发中，一般要遵循团队约定的代码规范。

不同的编程语言，都有一些著名的代码规范。例如著名的`K&R`是指《The C Programming Language》一书的作者`Kernighan`和`Ritchie`二人，这是世界上第一本介绍C语言的书，而`K&R风格`即指他们在该书中书写代码所使用的风格。

Google 有一个代码风格指引：[Google Style Guides](https://google.github.io/styleguide/)，里面包含了大部分主流编程语言的编码规范。以下`Python三引号字符串`摘录该规范的核心描述：

```python
google_style_guide = '''
Every major open-source project has its own style guide: a set of conventions (sometimes arbitrary) about how to write code for that project. It is much easier to understand a large codebase when all the code in it is in a consistent style.

“Style” covers a lot of ground, from “use camelCase for variable names” to “never use global variables” to “never use exceptions.” This project (google/styleguide) links to the style guidelines we use for Google code. If you are modifying a project that originated at Google, you may be pointed to this page to see the style guides that apply to that project.

This project holds the C++ Style Guide, C# Style Guide, Swift Style Guide, Objective-C Style Guide, Java Style Guide, Python Style Guide, R Style Guide, Shell Style Guide, HTML/CSS Style Guide, JavaScript Style Guide, TypeScript Style Guide, AngularJS Style Guide, Common Lisp Style Guide, and Vimscript Style Guide. This project also contains cpplint, a tool to assist with style guide compliance, and google-c-style.el, an Emacs settings file for Google style.
'''
```

CodeChina上有一个中文镜像仓库：[zh-google-styleguide](https://codechina.csdn.net/sj15102696860/zh-google-styleguide)，可以看到 `Google Python 代码风格指引`十分简短：[python_style_rules](https://google-styleguide.readthedocs.io/zh_CN/latest/google-python-styleguide/python_style_rules.html)

此外，Python 官方代码风格文档是：[PEP8](https://legacy.python.org/dev/peps/pep-0008/)。你会问`PEP`是什么？`PEP`是`Python Enhancement Proposals`的缩写。一个`PEP`是一份为Python社区提供各种增强功能的技术规格，也是提交新特性，以便让社区指出问题，精确化技术文档的提案。

实际的开发中可以通过配置开发环境的插件来辅助自动化检查代码风格。下面的`Python三引号字符串`描述了一组相关信息：

```python
python_style_guides = '''
* Python 代码风格指南',
    * [google-python-styleguide_zh_cn](https://zh-google-styleguide.readthedocs.io/en/latest/google-python-styleguide/python_style_rules /)
    * [PEP8](https://legacy.python.org/dev/peps/pep-0008/)
* 代码风格和自动完成工具链
    * 基本工具
        * [pylint](https://pylint.org/)
        * [autopep8](https://pypi.org/project/autopep8/)
    * Visual Studio Code Python 开发基本插件
        * Pylance
        * Python Path
        * Python-autopep8
'''
```

请编写一段单词统计Python代码，统计上述两个`Python三引号字符串`里英文单词的词频。要求：

* 单词请忽略大小写
* 使用数组`splits = ['\n', ' ', '-', ':', '/', '*', '_', '(', ')', '"', '”', '“',']','[']`来切割单词
* 输出词频最高的5个单词和词频信息。

基本代码框架如下：

```python

def top_words(splits, text, top_n=5):
    i = 0
    word_dict = {}
    chars = []
    while i < len(text):
        c = text[i]
        if c in splits:
            # 过滤掉分隔字符串
            while i+1 < len(text) and text[i+1] in splits:
                i += 1
            word = ''.join(chars).lower()

            # 统计词频
            # TODO(You): 请在此添加代码

            chars = []
        else:
            chars.append(c)

        i += 1

    word_list = list(word_dict.values())
    top_n = min(top_n, len(word_list))
    word_list.sort(key=lambda word_info: word_info['count'], reverse=True)
    return word_list[0:top_n]

if __name__ == '__main__':
    google_style_guide = ...
    python_style_guides = ...
    splits = [' ', '-', ':', '/', '*', '_', '(', ')', '"', '”', '“']

    tops = top_words(splits, google_style_guide+python_style_guides)

    print('单词排行榜')
    print('--------')
    i = 0
    while i < len(tops):
        top = tops[i]
        word = top['word']
        count = top['count']
        print(f'{i+1}. 单词：{word}, 词频：{count}')
        i += 1
```

预期的输出结果为：

```bash
单词排行榜
--------
1. 单词：style, 词频：20
2. 单词：guide,, 词频：13
3. 单词：to, 词频：9
4. 单词：python, 词频：8
5. 单词：google, 词频：7
```

以下选项是对代码中`TODO`部分的多种实现，你能找出以下实现<span style="color:red">错误</span>的选项吗？

## template

```python
def top_words(splits, text, top_n=5):
    i = 0
    word_dict = {}
    chars = []
    while i < len(text):
        c = text[i]
        if c in splits:
            while i+1 < len(text) and text[i+1] in splits:
                i += 1
            word = ''.join(chars).lower()

            word_info = word_dict.get(word, {'word': word, 'count': 0})
            word_info['count'] += 1
            word_dict[word] = word_info

            chars = []
        else:
            chars.append(c)

        i += 1

    word_list = list(word_dict.values())
    top_n = min(top_n, len(word_list))
    word_list.sort(key=lambda word_info: word_info['count'], reverse=True)
    return word_list[0:top_n]


if __name__ == '__main__':
    google_style_guide = '''
Every major open-source project has its own style guide: a set of conventions (sometimes arbitrary) about how to write code for that project. It is much easier to understand a large codebase when all the code in it is in a consistent style.

“Style” covers a lot of ground, from “use camelCase for variable names” to “never use global variables” to “never use exceptions.” This project (google/styleguide) links to the style guidelines we use for Google code. If you are modifying a project that originated at Google, you may be pointed to this page to see the style guides that apply to that project.

This project holds the C++ Style Guide, C# Style Guide, Swift Style Guide, Objective-C Style Guide, Java Style Guide, Python Style Guide, R Style Guide, Shell Style Guide, HTML/CSS Style Guide, JavaScript Style Guide, TypeScript Style Guide, AngularJS Style Guide, Common Lisp Style Guide, and Vimscript Style Guide. This project also contains cpplint, a tool to assist with style guide compliance, and google-c-style.el, an Emacs settings file for Google style.
'''

    python_style_guides = '''
* Python 代码风格指南',
    * [google-python-styleguide_zh_cn](https://zh-google-styleguide.readthedocs.io/en/latest/google-python-styleguide/python_style_rules /)
    * [PEP8](https://legacy.python.org/dev/peps/pep-0008/)
* 代码风格和自动完成工具链
    * 基本工具
        * [pylint](https://pylint.org/)
        * [autopep8](https://pypi.org/project/autopep8/)
    * Visual Studio Code Python 开发基本插件
        * Pylance
        * Python Path
        * Python-autopep8
'''

    splits = ['\n', ' ', '-', ':', '/', '*',
              '_', '(', ')', '"', '”', '“', '[', ']']

    tops = top_words(splits, google_style_guide+python_style_guides)

    print('单词排行榜')
    print('--------')
    i = 0
    while i < len(tops):
        top = tops[i]
        word = top['word']
        count = top['count']
        print(f'{i+1}. 单词：{word}, 词频：{count}')
        i += 1
```

## 答案

```python
if not word in word_dict:
    word_info = {'word': word, 'count': 0}
    word_dict[word] = word_info

word_info['count'] += 1
```

## 选项

### 如果没有就初始化词频个数为0，再统一自增

```python
word_info = word_dict.get(word)
if word_info is None:
    word_info = {'word': word, 'count': 0}
    word_dict[word] = word_info

word_info['count'] += 1
```

### 如果没有就初始化词频个数为1，否则自增

```python
word_info = word_dict.get(word)
if word_info is None:
    word_info = {'word': word, 'count': 1}
    word_dict[word] = word_info
else:
    word_info['count'] += 1
```

### 使用 Python 的 get 默认值

```python
word_info = word_dict.get(word, {'word': word, 'count': 0})
word_info['count'] += 1
word_dict[word] = word_info
```