jacksoncode.github.io/tutorials/python/71.html at master · jacksoncode/jacksoncode.github.io

Repository navigation

History

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

<!DOCTYPE html>

<head>

<title>16.3. argparse - CodeClub</title>

<style>

.tutorial-container { max-width: 960px; margin: 70px auto 40px; padding: 0 20px; }

.tutorial-sidebar { position: fixed; top: 70px; left: 20px; width: 260px; max-height: calc(100vh - 90px); overflow-y: auto; background: var(--bg-secondary, #fff); border-radius: 8px; padding: 16px; box-shadow: 0 2px 8px rgba(0,0,0,0.08); }

.tutorial-sidebar h3 { font-size: 16px; margin-bottom: 12px; color: var(--text-primary, #1a1a2e); }

.tutorial-sidebar a { display: block; padding: 6px 10px; color: var(--text-secondary, #666); text-decoration: none; font-size: 14px; border-radius: 4px; }

.tutorial-sidebar a:hover, .tutorial-sidebar a.active { background: var(--primary, #3b82f6); color: #fff; }

.tutorial-sidebar .sub-link { padding-left: 24px; font-size: 13px; }

.tutorial-content { margin-left: 300px; background: var(--bg-secondary, #fff); border-radius: 8px; padding: 32px; box-shadow: 0 2px 8px rgba(0,0,0,0.08); }

.tutorial-content h1 { font-size: 28px; margin-bottom: 20px; color: var(--text-primary, #1a1a2e); border-bottom: 2px solid var(--primary, #3b82f6); padding-bottom: 12px; }

.tutorial-content h2 { font-size: 22px; margin: 24px 0 16px; color: var(--text-primary, #1a1a2e); }

.tutorial-content h3 { font-size: 18px; margin: 20px 0 12px; }

.tutorial-content p { line-height: 1.8; margin: 12px 0; color: var(--text-secondary, #333); }

.tutorial-content pre { background: #1e1e2e; color: #cdd6f4; padding: 16px; border-radius: 8px; overflow-x: auto; margin: 16px 0; }

.tutorial-content code { font-family: 'Fira Code', 'Cascadia Code', monospace; font-size: 14px; }

.tutorial-content p code { background: #f1f5f9; padding: 2px 6px; border-radius: 4px; color: #e83e8c; }

.tutorial-content blockquote { border-left: 4px solid var(--primary, #3b82f6); padding: 12px 20px; margin: 16px 0; background: #f8fafc; border-radius: 0 8px 8px 0; }

.tutorial-content ul, .tutorial-content ol { padding-left: 24px; margin: 12px 0; }

.tutorial-content li { margin: 6px 0; line-height: 1.7; }

.tutorial-content img { max-width: 100%; border-radius: 8px; margin: 16px 0; }

.tutorial-nav { display: flex; justify-content: space-between; margin-top: 32px; padding-top: 20px; border-top: 1px solid var(--border, #e5e7eb); }

.tutorial-nav a { color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500; }

.tutorial-nav a:hover { text-decoration: underline; }

.tutorial-index { max-width: 960px; margin: 70px auto 40px; padding: 0 20px; }

.tutorial-card { background: var(--bg-secondary, #fff); border-radius: 12px; padding: 24px; margin: 16px 0; box-shadow: 0 2px 8px rgba(0,0,0,0.08); transition: transform 0.2s; }

.tutorial-card:hover { transform: translateY(-2px); }

.tutorial-card h3 { margin: 0 0 8px; color: var(--text-primary, #1a1a2e); }

.tutorial-card p { color: var(--text-secondary, #666); margin: 0 0 12px; }

.tutorial-card .badge { display: inline-block; padding: 4px 10px; border-radius: 20px; font-size: 12px; font-weight: 600; margin-right: 8px; }

.badge-python { background: #3b82f6; color: #fff; }

.badge-git { background: #f97316; color: #fff; }

.badge-ai { background: #8b5cf6; color: #fff; }

@media (max-width: 768px) {

.tutorial-sidebar { display: none; }

.tutorial-content { margin-left: 0; }

}

</style>

</head>

<body>

<span>CodeClub</span>

</a>

</button>

</ul>

</div>

</nav>

<div class="tutorial-container" style="max-width: 960px; margin: 80px auto 40px; padding: 0 20px;"><div class="tutorial-sidebar"><h3>目录</h3><a href="0.html">1. 简介</a><a href="1.html">2. Python历史</a><a href="2.html">3. 安装Python</a><a href="3.html">3.1. Python解释器</a><a href="4.html">4. 第一个Python程序</a><a href="5.html">4.1. 使用文本编辑器</a><a href="6.html">4.2. 输入和输出</a><a href="7.html">5. Python基础</a><a href="8.html">5.1. 数据类型和变量</a><a href="9.html">5.2. 字符串和编码</a><a href="10.html">5.3. 使用list和tuple</a><a href="11.html">5.4. 条件判断</a><a href="12.html">5.5. 模式匹配</a><a href="13.html">5.6. 循环</a><a href="14.html">5.7. 使用dict和set</a><a href="15.html">6. 函数</a><a href="16.html">6.1. 调用函数</a><a href="17.html">6.2. 定义函数</a><a href="18.html">6.3. 函数的参数</a><a href="19.html">6.4. 递归函数</a><a href="20.html">7. 高级特性</a><a href="21.html">7.1. 切片</a><a href="22.html">7.2. 迭代</a><a href="23.html">7.3. 列表生成式</a><a href="24.html">7.4. 生成器</a><a href="25.html">7.5. 迭代器</a><a href="26.html">8. 函数式编程</a><a href="27.html">8.1. 高阶函数</a><a href="28.html">8.1.1. map/reduce</a><a href="29.html">8.1.2. filter</a><a href="30.html">8.1.3. sorted</a><a href="31.html">8.2. 返回函数</a><a href="32.html">8.3. 匿名函数</a><a href="33.html">8.4. 装饰器</a><a href="34.html">8.5. 偏函数</a><a href="35.html">9. 模块</a><a href="36.html">9.1. 使用模块</a><a href="37.html">9.2. 安装第三方模块</a><a href="38.html">10. 面向对象编程</a><a href="39.html">10.1. 类和实例</a><a href="40.html">10.2. 访问限制</a><a href="41.html">10.3. 继承和多态</a><a href="42.html">10.4. 获取对象信息</a><a href="43.html">10.5. 实例属性和类属性</a><a href="44.html">11. 面向对象高级编程</a><a href="45.html">11.1. 使用__slots__</a><a href="46.html">11.2. 使用@property</a><a href="47.html">11.3. 多重继承</a><a href="48.html">11.4. 定制类</a><a href="49.html">11.5. 使用枚举类</a><a href="50.html">11.6. 使用元类</a><a href="51.html">12. 错误、调试和测试</a><a href="52.html">12.1. 错误处理</a><a href="53.html">12.2. 调试</a><a href="54.html">12.3. 单元测试</a><a href="55.html">12.4. 文档测试</a><a href="56.html">13. IO编程</a><a href="57.html">13.1. 文件读写</a><a href="58.html">13.2. StringIO和BytesIO</a><a href="59.html">13.3. 操作文件和目录</a><a href="60.html">13.4. 序列化</a><a href="61.html">14. 进程和线程</a><a href="62.html">14.1. 多进程</a><a href="63.html">14.2. 多线程</a><a href="64.html">14.3. ThreadLocal</a><a href="65.html">14.4. 进程 vs. 线程</a><a href="66.html">14.5. 分布式进程</a><a href="67.html">15. 正则表达式</a><a href="68.html">16. 常用内建模块</a><a href="69.html">16.1. datetime</a><a href="70.html">16.2. collections</a><a href="71.html">16.3. argparse</a><a href="72.html">16.4. base64</a><a href="73.html">16.5. struct</a><a href="74.html">16.6. hashlib</a><a href="75.html">16.7. hmac</a><a href="76.html">16.8. itertools</a><a href="77.html">16.9. contextlib</a><a href="78.html">16.10. urllib</a><a href="79.html">16.11. XML</a><a href="80.html">16.12. HTMLParser</a><a href="81.html">16.13. venv</a><a href="82.html">17. 常用第三方模块</a><a href="83.html">17.1. Pillow</a><a href="84.html">17.2. requests</a><a href="85.html">17.3. chardet</a><a href="86.html">17.4. psutil</a><a href="87.html">18. 图形界面</a><a href="88.html">18.1. 海龟绘图</a><a href="89.html">19. 网络编程</a><a href="90.html">19.1. TCP/IP简介</a><a href="91.html">19.2. TCP编程</a><a href="92.html">19.3. UDP编程</a><a href="93.html">20. 电子邮件</a><a href="94.html">20.1. SMTP发送邮件</a><a href="95.html">20.2. POP3收取邮件</a><a href="96.html">21. 访问数据库</a><a href="97.html">21.1. 使用SQLite</a><a href="98.html">21.2. 使用MySQL</a><a href="99.html">21.3. 使用SQLAlchemy</a><a href="100.html">22. Web开发</a><a href="101.html">22.1. HTTP协议简介</a><a href="102.html">22.2. HTML简介</a><a href="103.html">22.3. WSGI接口</a><a href="104.html">22.4. 使用Web框架</a><a href="105.html">22.5. 使用模板</a><a href="106.html">23. 异步IO</a><a href="107.html">23.1. 协程</a><a href="108.html">23.2. 使用asyncio</a><a href="109.html">23.3. 使用aiohttp</a><a href="110.html">24. FAQ</a><a href="111.html">25. 期末总结</a></div><div class="tutorial-content"><h1>16.3. argparse</h1><div class="tutorial-body"><pre class="hljs"><code class="language-python"><span class="hljs-comment"># copy.py</span>

<span class="hljs-keyword">import</span> sys

<span class="hljs-built_in">print</span>(sys.argv)

source = sys.argv[<span class="hljs-number">1</span>]

target = sys.argv[<span class="hljs-number">2</span>]

</code></pre>

<p>运行上述<code>copy.py</code>，并传入参数，打印如下：</p>

<pre class="hljs"><code class="language-plain">['copy.py', 'source.txt', 'copy.txt']

</code></pre>

<p>这种方式能应付简单的参数，但参数稍微复杂点，比如可以使用<code>-d</code>复制目录，使用<code>--filename *.py</code>过滤文件名等，解析起来就非常麻烦。</p>

<p>为了简化参数解析，我们可以使用内置的<a href="https://docs.python.org/3/library/argparse.html" target="_blank">argparse</a>库，定义好各个参数类型后，它能直接返回有效的参数。</p>

<p>假设我们想编写一个备份MySQL数据库的命令行程序，需要输入的参数如下：</p>

<ul>

<li>host参数：表示MySQL主机名或IP，不输入则默认为<code>localhost</code>；</li>

<li>port参数：表示MySQL的端口号，int类型，不输入则默认为<code>3306</code>；</li>

<li>user参数：表示登录MySQL的用户名，必须输入；</li>

<li>password参数：表示登录MySQL的口令，必须输入；</li>

<li>gz参数：表示是否压缩备份文件，不输入则默认为<code>False</code>；</li>

<li>outfile参数：表示备份文件保存在哪，必须输入。</li>

</ul>

<p>其中，<code>outfile</code>是位置参数，而其他则是类似<code>--user root</code>这样的“关键字”参数。</p>

<p>用<code>argparse</code>来解析参数，一个完整的示例如下：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-comment"># backup.py</span>

<span class="hljs-keyword">import</span> argparse

<span class="hljs-keyword">def</span> <span class="hljs-title function_">main</span>():

<span class="hljs-comment"># 定义一个ArgumentParser实例:</span>

parser = argparse.ArgumentParser(

prog=<span class="hljs-string">'backup'</span>, <span class="hljs-comment"># 程序名</span>

description=<span class="hljs-string">'Backup MySQL database.'</span>, <span class="hljs-comment"># 描述</span>

epilog=<span class="hljs-string">'Copyright(r), 2023'</span> <span class="hljs-comment"># 说明信息</span>

)

<span class="hljs-comment"># 定义位置参数:</span>

parser.add_argument(<span class="hljs-string">'outfile'</span>)

<span class="hljs-comment"># 定义关键字参数:</span>

parser.add_argument(<span class="hljs-string">'--host'</span>, default=<span class="hljs-string">'localhost'</span>)

<span class="hljs-comment"># 此参数必须为int类型:</span>

parser.add_argument(<span class="hljs-string">'--port'</span>, default=<span class="hljs-string">'3306'</span>, <span class="hljs-built_in">type</span>=<span class="hljs-built_in">int</span>)

<span class="hljs-comment"># 允许用户输入简写的-u:</span>

parser.add_argument(<span class="hljs-string">'-u'</span>, <span class="hljs-string">'--user'</span>, required=<span class="hljs-literal">True</span>)

parser.add_argument(<span class="hljs-string">'-p'</span>, <span class="hljs-string">'--password'</span>, required=<span class="hljs-literal">True</span>)

parser.add_argument(<span class="hljs-string">'--database'</span>, required=<span class="hljs-literal">True</span>)

<span class="hljs-comment"># gz参数不跟参数值，因此指定action='store_true'，意思是出现-gz表示True:</span>

parser.add_argument(<span class="hljs-string">'-gz'</span>, <span class="hljs-string">'--gzcompress'</span>, action=<span class="hljs-string">'store_true'</span>, required=<span class="hljs-literal">False</span>, <span class="hljs-built_in">help</span>=<span class="hljs-string">'Compress backup files by gz.'</span>)

args = parser.parse_args()

<span class="hljs-built_in">print</span>(<span class="hljs-string">'parsed args:'</span>)

<span class="hljs-built_in">print</span>(<span class="hljs-string">f'outfile = <span class="hljs-subst">{args.outfile}</span>'</span>)

<span class="hljs-built_in">print</span>(<span class="hljs-string">f'host = <span class="hljs-subst">{args.host}</span>'</span>)

<span class="hljs-built_in">print</span>(<span class="hljs-string">f'port = <span class="hljs-subst">{args.port}</span>'</span>)

<span class="hljs-built_in">print</span>(<span class="hljs-string">f'user = <span class="hljs-subst">{args.user}</span>'</span>)

<span class="hljs-built_in">print</span>(<span class="hljs-string">f'password = <span class="hljs-subst">{args.password}</span>'</span>)

<span class="hljs-built_in">print</span>(<span class="hljs-string">f'database = <span class="hljs-subst">{args.database}</span>'</span>)

<span class="hljs-built_in">print</span>(<span class="hljs-string">f'gzcompress = <span class="hljs-subst">{args.gzcompress}</span>'</span>)

<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:

main()

</code></pre>

<p>输入有效的参数，则程序能解析出所需的所有参数：</p>

<pre class="hljs"><code class="language-plain">$ ./backup.py -u root -p hello --database testdb backup.sql

parsed args:

outfile = backup.sql

host = localhost

port = 3306

user = root

password = hello

database = testdb

gzcompress = False

</code></pre>

<p>缺少必要的参数，或者参数不对，将报告详细的错误信息：</p>

<pre class="hljs"><code class="language-plain">$ ./backup.py --database testdb backup.sql

usage: backup [-h] [--host HOST] [--port PORT] -u USER -p PASSWORD --database DATABASE outfile

backup: error: the following arguments are required: -u/--user, -p/--password

</code></pre>

<p>更神奇的是，如果输入<code>-h</code>，则打印帮助信息：</p>

<pre class="hljs"><code class="language-plain">$ ./backup.py -h

usage: backup [-h] [--host HOST] [--port PORT] -u USER -p PASSWORD --database DATABASE outfile

Backup MySQL database.

positional arguments:

outfile

optional arguments:

-h, --help show this help message and exit

--host HOST

--port PORT

-u USER, --user USER

-p PASSWORD, --password PASSWORD

--database DATABASE

-gz, --gzcompress Compress backup files by gz.

</code></pre>

<p>获取有效参数的代码实际上是这一行：</p>

<pre class="hljs"><code class="language-python">args = parser.parse_args()

</code></pre>

<p>我们不必捕获异常，<code>parse_args()</code>非常方便的一点在于，如果参数有问题，则它打印出错误信息后，结束进程；如果参数是<code>-h</code>，则它打印帮助信息后，结束进程。只有当参数全部有效时，才会返回一个<a href="https://docs.python.org/3/library/argparse.html#argparse.Namespace" target="_blank">NameSpace</a>对象，获取对应的参数就把参数名当作属性获取，非常方便。</p>

<p>可见，使用<code>argparse</code>后，解析参数的工作被大大简化了，我们可以专注于定义参数，然后直接获取到有效的参数输入。</p>

<p>使用<a href="https://docs.python.org/3/library/argparse.html" target="_blank">argparse</a>解析参数，只需定义好参数类型，就可以获得有效的参数输入，能大大简化获取命令行参数的工作。</p>

</div>

<a href="/books/python/built-in-modules/collections/index.html"

onclick="gs_load_chapter('/books/python/built-in-modules/collections/index.html',true);return false;"

class="inline-block my-2">

stroke="currentColor">

<path stroke-linecap="round" stroke-linejoin="round"

d="M18.75 19.5l-7.5-7.5 7.5-7.5m-6 15L5.25 12l7.5-7.5" />

</svg>

collections

</a>

</div>

<a href="/books/python/built-in-modules/base64/index.html"

onclick="gs_load_chapter('/books/python/built-in-modules/base64/index.html',true);return false;"

class="inline-block my-2">

base64

stroke="currentColor">

<path stroke-linecap="round" stroke-linejoin="round"

d="M11.25 4.5l7.5 7.5-7.5 7.5m-6-15l7.5 7.5-7.5 7.5" />

</svg>

</a></div><div style="display: flex; justify-content: space-between; margin-top: 32px; padding-top: 20px; border-top: 1px solid var(--border, #e5e7eb);"><a href="70.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">← 16.2. collections</a><a href="72.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">16.4. base64 →</a></div><p style="margin-top: 16px; font-size: 13px; color: var(--text-secondary, #999);">原文：<a href="https://liaoxuefeng.com/books/python/built-in-modules/argparse/index.html" style="color: var(--primary, #3b82f6);">廖雪峰 - 16.3. argparse</a></p></div></div>

</div>

</footer>

</body>

</html>

FilesExpand file tree

71.html

Latest commit

History

71.html

File metadata and controls