jacksoncode.github.io/tutorials/python/46.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

<!DOCTYPE html>

<head>

<title>11.2. 使用@property - 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>11.2. 使用@property</h1><div class="tutorial-body"><pre class="hljs"><code class="language-python">s = Student()

s.score = <span class="hljs-number">9999</span>

</code></pre>

<p>这显然不合逻辑。为了限制<code>score</code>的范围，可以通过一个<code>set_score()</code>方法来设置成绩，再通过一个<code>get_score()</code>来获取成绩，这样，在<code>set_score()</code>方法里，就可以检查参数：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Student</span>(<span class="hljs-title class_ inherited__">object</span>):

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

<span class="hljs-keyword">return</span> <span class="hljs-variable language_">self</span>._score

<span class="hljs-keyword">def</span> <span class="hljs-title function_">set_score</span>(<span class="hljs-params">self, value</span>):

<span class="hljs-keyword">if</span> <span class="hljs-keyword">not</span> <span class="hljs-built_in">isinstance</span>(value, <span class="hljs-built_in">int</span>):

<span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'score must be an integer!'</span>)

<span class="hljs-keyword">if</span> value < <span class="hljs-number">0</span> <span class="hljs-keyword">or</span> value > <span class="hljs-number">100</span>:

<span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'score must between 0 ~ 100!'</span>)

<span class="hljs-variable language_">self</span>._score = value

</code></pre>

<p>现在，对任意的<code>Student</code>实例进行操作，就不能随心所欲地设置<code>score</code>了：</p>

<pre class="hljs"><code class="language-plain">>>> s = Student()

>>> s.set_score(60) # ok!

>>> s.get_score()

>>> s.set_score(9999)

Traceback (most recent call last):

...

ValueError: score must between 0 ~ 100!

</code></pre>

<p>但是，上面的调用方法又略显复杂，没有直接用属性这么直接简单。</p>

<p>有没有既能检查参数，又可以用类似属性这样简单的方式来访问类的变量呢？对于追求完美的Python程序员来说，这是必须要做到的！</p>

<p>还记得装饰器（decorator）可以给函数动态加上功能吗？对于类的方法，装饰器一样起作用。Python内置的<code>@property</code>装饰器就是负责把一个方法变成属性调用的：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Student</span>(<span class="hljs-title class_ inherited__">object</span>):

<span class="hljs-meta"> @property</span>

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

<span class="hljs-keyword">return</span> <span class="hljs-variable language_">self</span>._score

<span class="hljs-meta"> @score.setter</span>

<span class="hljs-keyword">def</span> <span class="hljs-title function_">score</span>(<span class="hljs-params">self, value</span>):

<span class="hljs-keyword">if</span> <span class="hljs-keyword">not</span> <span class="hljs-built_in">isinstance</span>(value, <span class="hljs-built_in">int</span>):

<span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'score must be an integer!'</span>)

<span class="hljs-keyword">if</span> value < <span class="hljs-number">0</span> <span class="hljs-keyword">or</span> value > <span class="hljs-number">100</span>:

<span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'score must between 0 ~ 100!'</span>)

<span class="hljs-variable language_">self</span>._score = value

</code></pre>

<p><code>@property</code>的实现比较复杂，我们先考察如何使用。把一个getter方法变成属性，只需要加上<code>@property</code>就可以了，此时，<code>@property</code>本身又创建了另一个装饰器<code>@score.setter</code>，负责把一个setter方法变成属性赋值，于是，我们就拥有一个可控的属性操作：</p>

<pre class="hljs"><code class="language-plain">>>> s = Student()

>>> s.score = 60 # OK，实际转化为s.score(60)

>>> s.score # OK，实际转化为s.score()

>>> s.score = 9999

Traceback (most recent call last):

...

ValueError: score must between 0 ~ 100!

</code></pre>

<p>注意到这个神奇的<code>@property</code>，我们在对实例属性操作的时候，就知道该属性很可能不是直接暴露的，而是通过getter和setter方法来实现的。</p>

<p>还可以定义只读属性，只定义getter方法，不定义setter方法就是一个只读属性：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Student</span>(<span class="hljs-title class_ inherited__">object</span>):

<span class="hljs-meta"> @property</span>

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

<span class="hljs-keyword">return</span> <span class="hljs-variable language_">self</span>._birth

<span class="hljs-meta"> @birth.setter</span>

<span class="hljs-keyword">def</span> <span class="hljs-title function_">birth</span>(<span class="hljs-params">self, value</span>):

<span class="hljs-variable language_">self</span>._birth = value

<span class="hljs-meta"> @property</span>

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

<span class="hljs-keyword">return</span> <span class="hljs-number">2015</span> - <span class="hljs-variable language_">self</span>._birth

</code></pre>

<p>上面的<code>birth</code>是可读写属性，而<code>age</code>就是一个<em>只读</em>属性，因为<code>age</code>可以根据<code>birth</code>和当前时间计算出来。</p>

<p>要特别注意：属性的方法名不要和实例变量重名。例如，以下的代码是错误的：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Student</span>(<span class="hljs-title class_ inherited__">object</span>):

<span class="hljs-comment"># 方法名称和实例变量均为birth:</span>

<span class="hljs-meta"> @property</span>

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

<span class="hljs-keyword">return</span> <span class="hljs-variable language_">self</span>.birth

</code></pre>

<p>这是因为调用<code>s.birth</code>时，首先转换为方法调用，在执行<code>return self.birth</code>时，又视为访问<code>self</code>的属性，于是又转换为方法调用<code>self.birth()</code>，造成无限递归，最终导致栈溢出报错<code>RecursionError</code>。</p>

<p>属性方法名和实例变量重名，会造成递归调用，导致栈溢出报错！

</p></div>

<p><code>@property</code>广泛应用在类的定义中，可以让调用者写出简短的代码，同时保证对参数进行必要的检查，这样，程序运行时就减少了出错的可能性。</p>

<p>请利用<code>@property</code>给一个<code>Screen</code>对象加上<code>width</code>和<code>height</code>属性，以及一个只读属性<code>resolution</code>：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Screen</span>(<span class="hljs-title class_ inherited__">object</span>):

s = Screen()

s.width = <span class="hljs-number">1024</span>

s.height = <span class="hljs-number">768</span>

<span class="hljs-built_in">print</span>(<span class="hljs-string">'resolution ='</span>, s.resolution)

<span class="hljs-keyword">if</span> s.resolution == <span class="hljs-number">786432</span>:

<span class="hljs-built_in">print</span>(<span class="hljs-string">'测试通过!'</span>)

<span class="hljs-keyword">else</span>:

<span class="hljs-built_in">print</span>(<span class="hljs-string">'测试失败!'</span>)

</code></pre>

<p><a href="use_property.py">use_property.py</a></p>

</div>

<a href="/books/python/oop-adv/slots/index.html"

onclick="gs_load_chapter('/books/python/oop-adv/slots/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>

使用__slots__

</a>

</div>

<a href="/books/python/oop-adv/multi-inheritance/index.html"

onclick="gs_load_chapter('/books/python/oop-adv/multi-inheritance/index.html',true);return false;"

class="inline-block my-2">

多重继承

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="45.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">← 11.1. 使用__slots__</a><a href="47.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">11.3. 多重继承 →</a></div><p style="margin-top: 16px; font-size: 13px; color: var(--text-secondary, #999);">原文：<a href="https://liaoxuefeng.com/books/python/oop-adv/property/index.html" style="color: var(--primary, #3b82f6);">廖雪峰 - 11.2. 使用@property</a></p></div></div>

</div>

</footer>

</body>

</html>

FilesExpand file tree

46.html

Latest commit

History

46.html

File metadata and controls