你有两种选择：使用嵌套作用域，或者使用可调用对象。 例如，假设你想要定义 linear(a,b) 使其返回一个函数 f(x) 来设计 a*x+b 的值。 可以使用以下嵌套作用域:
<span class="k">def</span> <span class="nf">linear</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">result</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
<span class="k">return</span> <span class="n">a</span> <span class="o">*</span> <span class="n">x</span> <span class="o">+</span> <span class="n">b</span>
<span class="k">return</span> <span class="n">result</span>
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或使用一个可调用对象:
<span class="k">class</span> <span class="nc">linear</span><span class="p">:</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">a</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span> <span class="o">=</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span>
<span class="k">def</span> <span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span> <span class="o">*</span> <span class="n">x</span> <span class="o">+</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span>
在两种情况下，:
<span class="n">taxes</span> <span class="o">=</span> <span class="n">linear</span><span class="p">(</span><span class="mf">0.3</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
都会给出一个可调用对象，使得 taxes(10e6) == 0.3 * 10e6 + 2.
可调用对象方式的缺点是速度略慢且生成的代码略长。 但是，请注意一组可调用对象能够通过继承来共享签名:
<span class="k">class</span> <span class="nc">exponential</span><span class="p">(</span><span class="n">linear</span><span class="p">):</span>
<span class="c1"># __init__ inherited</span>
<span class="k">def</span> <span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span> <span class="o">*</span> <span class="p">(</span><span class="n">x</span> <span class="o">**</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span><span class="p">)</span>
对象可以封装多个方法的状态:
<span class="k">class</span> <span class="nc">counter</span><span class="p">:</span>
<span class="n">value</span> <span class="o">=</span> <span class="mi">0</span>
<span class="k">def</span> <span class="nf">set</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">=</span> <span class="n">x</span>
<span class="k">def</span> <span class="nf">up</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">+</span> <span class="mi">1</span>
<span class="k">def</span> <span class="nf">down</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">-</span> <span class="mi">1</span>
<span class="n">count</span> <span class="o">=</span> <span class="n">counter</span><span class="p">()</span>
<span class="n">inc</span><span class="p">,</span> <span class="n">dec</span><span class="p">,</span> <span class="n">reset</span> <span class="o">=</span> <span class="n">count</span><span class="o">.</span><span class="n">up</span><span class="p">,</span> <span class="n">count</span><span class="o">.</span><span class="n">down</span><span class="p">,</span> <span class="n">count</span><span class="o">.</span><span class="n">set</span>
这里 inc(), dec() 和 reset() 将表现为共享同一计数变量的多个函数。
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转载请注明原文链接：python如何创建高阶函数？
转载请注明原文链接：python如何创建高阶函数？
