Home >Backend Development >Python Tutorial >python idle 解释和直接 python script.py 解释有什么差别?

python idle 解释和直接 python script.py 解释有什么差别?

WBOY
WBOYOriginal
2016-06-06 16:22:181529browse

回复内容:

题主想的“逐行解释”与“整体解释”的差异的思路是对的,不过细节不太对。下面讲点细节。
跟Sublime、IDLE啥的没关系。

<code class="language-python"><span class="err">$</span> <span class="n">python</span>
<span class="n">Python</span> <span class="mf">2.7</span><span class="o">.</span><span class="mi">5</span> <span class="p">(</span><span class="n">default</span><span class="p">,</span> <span class="n">Mar</span>  <span class="mi">9</span> <span class="mi">2014</span><span class="p">,</span> <span class="mi">22</span><span class="p">:</span><span class="mi">15</span><span class="p">:</span><span class="mo">05</span><span class="p">)</span> 
<span class="p">[</span><span class="n">GCC</span> <span class="mf">4.2</span><span class="o">.</span><span class="mi">1</span> <span class="n">Compatible</span> <span class="n">Apple</span> <span class="n">LLVM</span> <span class="mf">5.0</span> <span class="p">(</span><span class="n">clang</span><span class="o">-</span><span class="mf">500.0</span><span class="o">.</span><span class="mi">68</span><span class="p">)]</span> <span class="n">on</span> <span class="n">darwin</span>
<span class="n">Type</span> <span class="s">"help"</span><span class="p">,</span> <span class="s">"copyright"</span><span class="p">,</span> <span class="s">"credits"</span> <span class="ow">or</span> <span class="s">"license"</span> <span class="k">for</span> <span class="n">more</span> <span class="n">information</span><span class="o">.</span>
<span class="o">>>></span> <span class="n">a</span> <span class="o">=</span> <span class="mf">10.1</span>
<span class="o">>>></span> <span class="n">b</span> <span class="o">=</span> <span class="mf">10.1</span>
<span class="o">>>></span> <span class="n">a</span> <span class="ow">is</span> <span class="n">b</span>
<span class="bp">False</span>
<span class="o">>>></span> <span class="nb">id</span><span class="p">(</span><span class="n">a</span><span class="p">)</span>
<span class="mi">140475784803760</span>
<span class="o">>>></span> <span class="nb">id</span><span class="p">(</span><span class="n">b</span><span class="p">)</span>
<span class="mi">140475784803736</span>
<span class="o">>>></span> <span class="p">(</span><span class="mf">10.1</span><span class="p">)</span> <span class="ow">is</span> <span class="p">(</span><span class="mf">10.1</span><span class="p">)</span>
<span class="bp">True</span>
<span class="o">>>></span> <span class="k">def</span> <span class="nf">foo</span><span class="p">():</span>
<span class="o">...</span>   <span class="n">a</span> <span class="o">=</span> <span class="mf">10.1</span>
<span class="o">...</span>   <span class="n">b</span> <span class="o">=</span> <span class="mf">10.1</span>
<span class="o">...</span>   <span class="k">return</span> <span class="n">a</span> <span class="ow">is</span> <span class="n">b</span>
<span class="o">...</span> 
<span class="o">>>></span> <span class="n">foo</span><span class="p">()</span>
<span class="bp">True</span>
</code>
is 是判断identity的,如果两个变量 id (address)相同,那么a is b就是True;
所以从执行结果来看,也是符合的。

至于问题中的差别,那就是实现相关的,像10.1这样的small number是否再次赋值会复用id那是实现相关的(我的2.7.6是不同的id);我估计可能sublime本身内置有python的运行时(不太确定,我不大用sublime),所以会出现不同的表现。 给自己埋个坑,今天突然想到了一种可能,由于IDLE是逐条解释命令的,而python中的浮点数保存在堆内存中,每次创建一个浮点数,都会直接将堆内存地址压栈,创建相同浮点数时,IDLE也会执行重复动作;而当写到脚本中,用解释器执行时,碰到简单的数值对象,就会检查是否已经存在该对象(数值对象重复判断比较简单),从而直接将存在的堆地址压栈即可。
应该是python的解释器存在朱涛所说的运行时,究竟如何要以后看了解释器的实现过程才明白了。等以后填坑。
Statement:
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn