python attrgetter()__python

<code class="hljs python has-numbering"><span class="hljs-comment"># -*- coding: utf-8 -*-</span><span class="hljs-comment"># 在排序時, 可以用lambda運算式將對象map成keys</span><span class="hljs-comment"># 亦可以使用operator包中的attrgetter和itemgetter函數以提高效率</span><span class="hljs-comment"># 參考 http://wiki.python.org/moin/HowTo/Sorting</span><span class="hljs-comment"># 考慮 Student 對象</span><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Student</span>:</span>    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name, grade, age)</span>:</span>            self.name = name            self.grade = grade            self.age = age    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__repr__</span><span class="hljs-params">(self)</span>:</span>            <span class="hljs-keyword">return</span> repr((self.name, self.grade, self.age))<span class="hljs-comment"># 建立一組Student對象</span>students = [    Student(<span class="hljs-string">'jane'</span>, <span class="hljs-string">'B'</span>, <span class="hljs-number">12</span>),    Student(<span class="hljs-string">'john'</span>, <span class="hljs-string">'A'</span>, <span class="hljs-number">12</span>),    Student(<span class="hljs-string">'dave'</span>, <span class="hljs-string">'B'</span>, <span class="hljs-number">10</span>),]<span class="hljs-keyword">from</span> operator <span class="hljs-keyword">import</span> itemgetter, attrgetter<span class="hljs-comment"># 對students按照年齡排序</span><span class="hljs-keyword">print</span> sorted(students, key=attrgetter(<span class="hljs-string">'age'</span>))<span class="hljs-comment"># 其等價於</span><span class="hljs-keyword">print</span> sorted(students, key=<span class="hljs-keyword">lambda</span> o: o.age)<span class="hljs-comment"># 輸出: >>> [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]</span><span class="hljs-comment"># 亦可以按多個key排序, 先按age再按grade排序</span><span class="hljs-keyword">print</span> sorted(students, key=attrgetter(<span class="hljs-string">'age'</span>, <span class="hljs-string">'grade'</span>))<span class="hljs-comment"># 輸出: >>> [('dave', 'B', 10), ('john', 'A', 12), ('jane', 'B', 12)]</span></code>