三十4、Python面向对象："假"封装
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<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;">Python面向对象三大特征之封装</p>
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<h1 style="color: black; text-align: left; margin-bottom: 10px;">1.什么是封装？</h1>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;">众所周知，封装(Encapsulation)、继承(Inherit)和多态(Polymorphism)是面向对象的三大特征，它指的是将对象的状态信息<span style="color: black;">隐匿</span>在类定义的内部，不<span style="color: black;">准许</span>外界直接<span style="color: black;">拜访</span>对象的内部信息，而是<span style="color: black;">经过</span>该类对<span style="color: black;">外边</span>暴露的<span style="color: black;">办法</span>来实现对类内部信息的<span style="color: black;">拜访</span>和操作。</p>
<h1 style="color: black; text-align: left; margin-bottom: 10px;">2.封装的好处</h1>对外<span style="color: black;">隐匿</span>类内部的实现细节；<span style="color: black;">运用</span>者仅通<span style="color: black;">经过</span>类定义时对外暴露的<span style="color: black;">办法</span>来<span style="color: black;">拜访</span>数据，<span style="color: black;">因此呢</span>，<span style="color: black;">能够</span>在定义<span style="color: black;">办法</span>时添加<span style="color: black;">掌控</span><span style="color: black;">规律</span>，限制对属性的不<span style="color: black;">恰当</span><span style="color: black;">拜访</span>；在用户<span style="color: black;">经过</span><span style="color: black;">办法</span>设置或修改类的属性时，<span style="color: black;">能够</span>在<span style="color: black;">办法</span>上添加数据校验规则，<span style="color: black;">能够</span><span style="color: black;">保准</span>数据的完整性和有效性；<h1 style="color: black; text-align: left; margin-bottom: 10px;">3.<span style="color: black;">怎么样</span>实现封装？</h1>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;">实现封装<span style="color: black;">能够</span>从以下两方面来<span style="color: black;">思虑</span>：</p><span style="color: black;">必须</span>将对象的属性和实现细节<span style="color: black;">隐匿</span>起来，不<span style="color: black;">准许</span><span style="color: black;">外边</span>直接<span style="color: black;">拜访</span>和操作；将<span style="color: black;">办法</span>暴露出来，让<span style="color: black;">办法</span>来<span style="color: black;">掌控</span>这些属性的<span style="color: black;">拜访</span>与操作；<h1 style="color: black; text-align: left; margin-bottom: 10px;">4.Python类中实现封装</h1>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">由于</span>Python是解释型的语言，并<span style="color: black;">无</span>像其它语言<span style="color: black;">供给</span>变量的修饰符，<span style="color: black;">例如</span>private, protected等，而是<span style="color: black;">经过</span>一种技巧，即Python内部的约定，给类成员命名以双下划线的开头，Python就会将它们<span style="color: black;">隐匿</span>起来。</p><span style="color: black;"><span style="color: black;">class</span> <span style="color: black;">Dog</span>:</span>
<span style="color: black;"><span style="color: black;">def</span> <span style="color: black;">get_name</span><span style="color: black;">(<span style="color: black;">self</span>)</span></span>:
<span style="color: black;">return</span> <span style="color: black;">self</span>.__name
<span style="color: black;"><span style="color: black;">def</span> <span style="color: black;">set_name</span><span style="color: black;">(<span style="color: black;">self</span>, name)</span></span>:
<span style="color: black;">if</span>(len(name)<<span style="color: black;">2</span>):
raise ValueError(<span style="color: black;">狗的名字<span style="color: black;">最少</span><span style="color: black;">必须</span>两个汉字</span>)<span style="color: black;">self</span>.__name = name
name = property(get_name, set_name)
<span style="color: black;"><span style="color: black;">def</span> <span style="color: black;">__pee</span><span style="color: black;">(<span style="color: black;">self</span>)</span></span>:
print(<span style="color: black;">我要尿尿了...</span>)
<span style="color: black;"># 实例化并调用</span>
d = Dog()
<span style="color: black;"># 尝试直接给变量赋值</span>
d.name = <span style="color: black;">泰迪</span>
print(d.name)
<span style="color: black;">#d.name =狗</span>
<span style="color: black;">#print(d.name) # ValueError: 狗的名字<span style="color: black;">最少</span><span style="color: black;">必须</span>两个汉字</span>
<span style="color: black;">#d.__pee() # AttributeError: Dog object has no attribute __pee</span>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;">上面的例子中将Dog类的实例变量命名为__name, 这个实例变量就会被<span style="color: black;">隐匿</span>起来，<span style="color: black;">这般</span>，程序<span style="color: black;">没法</span>直接<span style="color: black;">拜访</span>该实例变量，只能<span style="color: black;">经过</span>get_name, set_name这些<span style="color: black;">办法</span>来进行<span style="color: black;">拜访</span>, 而get_name, set_name会添加<span style="color: black;">掌控</span><span style="color: black;">规律</span>，<span style="color: black;">仅有</span>符合<span style="color: black;">要求</span>的name才<span style="color: black;">准许</span>被设置。</p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">另一</span>，<span style="color: black;">针对</span><span style="color: black;">隐匿</span>的<span style="color: black;">办法</span>__pee(), 程序尝试执行，<span style="color: black;">因为</span>该<span style="color: black;">办法</span>在类的内部定义为<span style="color: black;">隐匿</span>，<span style="color: black;">因此</span>直接<span style="color: black;">拜访</span>会报错。</p>
<h1 style="color: black; text-align: left; margin-bottom: 10px;">5.<span style="color: black;">为何</span>说Python中的封装是“假”封装？</h1>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;">其实，Python其实<span style="color: black;">无</span>真正的<span style="color: black;">隐匿</span>机制，双下划线实现<span style="color: black;">隐匿</span>在Python中只是一种技巧, <span style="color: black;">由于</span><span style="color: black;">针对</span>加了双下划线的变量和<span style="color: black;">办法</span>名，Python会巧妙地改名这个名字，即会在你定义的双下划线变量或<span style="color: black;">办法</span>前再添加单下划线和类名。<span style="color: black;">能够</span><span style="color: black;">经过</span>"<strong style="color: blue;">对象名.__dict__</strong>"查看，或<span style="color: black;">经过</span>"<strong style="color: blue;">对象名._类名__[<span style="color: black;">办法</span>名|变量名]</strong>"调用:</p><span style="color: black;"><span style="color: black;">class</span> <span style="color: black;">Dog</span>:</span>
<span style="color: black;"><span style="color: black;">def</span> <span style="color: black;">get_name</span><span style="color: black;">(<span style="color: black;">self</span>)</span></span>:
<span style="color: black;">return</span> <span style="color: black;">self</span>.__name
<span style="color: black;"><span style="color: black;">def</span> <span style="color: black;">set_name</span><span style="color: black;">(<span style="color: black;">self</span>, name)</span></span>:
<span style="color: black;">if</span>(len(name)<<span style="color: black;">2</span>):
raise ValueError(<span style="color: black;">狗的名字<span style="color: black;">最少</span><span style="color: black;">必须</span>两个汉字</span>)
<span style="color: black;">self</span>.__name = name
name = property(get_name, set_name)<span style="color: black;"><span style="color: black;">def</span> <span style="color: black;">__pee</span><span style="color: black;">(<span style="color: black;">self</span>)</span></span>:
print(<span style="color: black;">我要尿尿了...</span>)
<span style="color: black;"># 实例化并调用</span>
d = Dog()
d.name =<span style="color: black;">泰迪</span>
<span style="color: black;"># <span style="color: black;">经过</span>下面的<span style="color: black;">办法</span><span style="color: black;">能够</span>查看被<span style="color: black;">隐匿</span>的成员变量和<span style="color: black;">办法</span></span>print(d._Dog__name)
d._Dog__name=<span style="color: black;">藏獒</span>
print(d._Dog__name)
d._Dog__pee()<div style="color: black; text-align: left; margin-bottom: 10px;"><img src="https://p3-sign.toutiaoimg.com/pgc-image/394eb2f74b8347bfa7317a6612f730df~noop.image?_iz=58558&from=article.pc_detail&lk3s=953192f4&x-expires=1723895751&x-signature=P4RJAu3XbBeDNCynqt4zZzFzlM8%3D" style="width: 50%; margin-bottom: 20px;">
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;">查看<span style="color: black;">隐匿</span>变量和<span style="color: black;">办法</span></p>
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<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">因此</span>，从上面<span style="color: black;">能够</span>看出，Python并<span style="color: black;">无</span>真正地实现“<span style="color: black;">隐匿</span>”机制，是一种“<strong style="color: blue;">假</strong>”封装，<span style="color: black;">然则</span><span style="color: black;">咱们</span>不<span style="color: black;">举荐</span><span style="color: black;">这般</span><span style="color: black;">拜访</span>，<span style="color: black;">一般</span><span style="color: black;">亦</span>不会这么<span style="color: black;">拜访</span>。</p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">因此</span>，<span style="color: black;">倘若</span><span style="color: black;">必须</span><span style="color: black;">隐匿</span>变量或成员<span style="color: black;">办法</span>，<span style="color: black;">能够</span><span style="color: black;">运用</span>以“双下划线”命名的这种方式，Python<span style="color: black;">亦</span><span style="color: black;">举荐</span>这种<span style="color: black;">运用</span>方式。</p>
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