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index 966a1b5..34d3462 100644
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+++ b/LectureNotesOnPython.html
@@ -377,41 +377,48 @@ ul.auto-toc {
<div class="contents topic" id="id1">
<p class="topic-title first">内容目录</p>
<ul class="simple">
-<li><a class="reference internal" href="#python" id="id12">Python的发音纠正</a></li>
-<li><a class="reference internal" href="#id2" id="id13">Python源流</a></li>
-<li><a class="reference internal" href="#id3" id="id14">Python的关键词</a></li>
-<li><a class="reference internal" href="#id4" id="id15">值的类型</a></li>
-<li><a class="reference internal" href="#variable" id="id16">变量(Variable)</a></li>
-<li><a class="reference internal" href="#mutable" id="id17">可变(mutable)类型与不可变类型</a></li>
-<li><a class="reference internal" href="#id5" id="id18">数与格式化显示</a></li>
-<li><a class="reference internal" href="#strings" id="id19">字符串(Strings)</a></li>
-<li><a class="reference internal" href="#concatenation" id="id20">字符串相加(concatenation)</a></li>
-<li><a class="reference internal" href="#slice" id="id21">子串(slice)</a></li>
-<li><a class="reference internal" href="#id6" id="id22">搜索字符串</a></li>
-<li><a class="reference internal" href="#string" id="id23">String类(对象)方法</a></li>
-<li><a class="reference internal" href="#in" id="id24">in操作符</a></li>
-<li><a class="reference internal" href="#id7" id="id25">字符串比较</a></li>
-<li><a class="reference internal" href="#id8" id="id26">列表</a></li>
-<li><a class="reference internal" href="#id9" id="id27">列表作为参数</a></li>
-<li><a class="reference internal" href="#append" id="id28">注意区别 <tt class="docutils literal">append</tt> 与 <tt class="docutils literal">+</tt> 操作符</a><ul>
-<li><a class="reference internal" href="#tdd-test-driven-development" id="id29">TDD - Test-driven Development</a></li>
-<li><a class="reference internal" href="#id10" id="id30">计算复杂度</a></li>
+<li><a class="reference internal" href="#python" id="id16">Python的发音纠正</a></li>
+<li><a class="reference internal" href="#id2" id="id17">Python源流</a></li>
+<li><a class="reference internal" href="#id3" id="id18">Python的关键词</a></li>
+<li><a class="reference internal" href="#id4" id="id19">值的类型</a></li>
+<li><a class="reference internal" href="#variable" id="id20">变量(Variable)</a></li>
+<li><a class="reference internal" href="#mutable" id="id21">可变(mutable)类型与不可变类型</a></li>
+<li><a class="reference internal" href="#id5" id="id22">数与格式化显示</a></li>
+<li><a class="reference internal" href="#strings" id="id23">字符串(Strings)</a></li>
+<li><a class="reference internal" href="#concatenation" id="id24">字符串相加(concatenation)</a></li>
+<li><a class="reference internal" href="#slice" id="id25">子串(slice)</a></li>
+<li><a class="reference internal" href="#id6" id="id26">搜索字符串</a></li>
+<li><a class="reference internal" href="#string" id="id27">String类(对象)方法</a></li>
+<li><a class="reference internal" href="#in" id="id28">in操作符</a></li>
+<li><a class="reference internal" href="#id7" id="id29">字符串比较</a></li>
+<li><a class="reference internal" href="#id8" id="id30">列表</a></li>
+<li><a class="reference internal" href="#id9" id="id31">列表作为参数</a></li>
+<li><a class="reference internal" href="#append" id="id32">注意区别 <tt class="docutils literal">append</tt> 与 <tt class="docutils literal">+</tt> 操作符</a><ul>
+<li><a class="reference internal" href="#tdd-test-driven-development" id="id33">TDD - Test-driven Development</a></li>
+<li><a class="reference internal" href="#id10" id="id34">计算复杂度</a></li>
</ul>
</li>
-<li><a class="reference internal" href="#dictionary" id="id31">字典(Dictionary)</a><ul>
-<li><a class="reference internal" href="#incremental-development" id="id32">递增开发(Incremental Development)</a></li>
+<li><a class="reference internal" href="#dictionary" id="id35">字典(Dictionary)</a><ul>
+<li><a class="reference internal" href="#incremental-development" id="id36">递增开发(Incremental Development)</a></li>
+<li><a class="reference internal" href="#keyvalue" id="id37">key与value互换</a></li>
</ul>
</li>
-<li><a class="reference internal" href="#id11" id="id33">参考</a></li>
+<li><a class="reference internal" href="#id11" id="id38">函数</a><ul>
+<li><a class="reference internal" href="#id12" id="id39">局部变量</a></li>
+<li><a class="reference internal" href="#id13" id="id40">全局变量</a></li>
+<li><a class="reference internal" href="#id14" id="id41">函数执行顺序</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#id15" id="id42">参考</a></li>
</ul>
</div>
<div class="section" id="python">
-<h1><a class="toc-backref" href="#id12">Python的发音纠正</a></h1>
+<h1><a class="toc-backref" href="#id16">Python的发音纠正</a></h1>
<p>国人普遍把th发作s。 Not quite correct。</p>
<p>ˈpī-ˌthän , -thən <a class="reference external" href="https://cn.bing.com/search?q=define%20python&amp;tf=U2VydmljZT1EaWN0aW9uYXJ5QW5zd2VyVjIgU2NlbmFyaW89RGVmaW5pdGlvblNjZW5hcmlvIFBvc2l0aW9uPU5PUCBSYW5raW5nRGF0YT1UcnVlIEZvcmNlUGxhY2U9RmFsc2UgUGFpcnM9RGljdGlvbmFyeVdvcmQ6cHl0aG9uO3NjbjpEZWZpbml0aW9uU2NlbmFyaW87cDpRQVM7IHw%3d&amp;hs=hyRBF0mYq9hrfQUq66DIZnFVta1ZGRfBiBks25oUguk%3d">pronounciation</a></p>
</div>
<div class="section" id="id2">
-<h1><a class="toc-backref" href="#id13">Python源流</a></h1>
+<h1><a class="toc-backref" href="#id17">Python源流</a></h1>
<p>Python之父Guido van Rossum,荷兰人,1956年生,1982年阿姆斯特丹大学获得
数学与计算机科学硕士学位。有过ABC语言的工作经验。1989年设计了Python语
言。</p>
@@ -461,7 +468,7 @@ ul.auto-toc {
</blockquote>
</div>
<div class="section" id="id3">
-<h1><a class="toc-backref" href="#id14">Python的关键词</a></h1>
+<h1><a class="toc-backref" href="#id18">Python的关键词</a></h1>
<div class="line-block">
<div class="line">def pass</div>
<div class="line">from import</div>
@@ -483,7 +490,7 @@ ul.auto-toc {
<p>关键词被语言留用(reserved),无法作变量名。</p>
</div>
<div class="section" id="id4">
-<h1><a class="toc-backref" href="#id15">值的类型</a></h1>
+<h1><a class="toc-backref" href="#id19">值的类型</a></h1>
<p>所有的值都是对象。a = 5, help(a) a.bit_length()</p>
<p>数字。1, 1.,1.1, .1, 1e1, 1e-1, 1E1, 1E-1</p>
<dl class="docutils">
@@ -503,7 +510,7 @@ A list of objects</dd>
<p>元组(tuple),字典(dict)。</p>
</div>
<div class="section" id="variable">
-<h1><a class="toc-backref" href="#id16">变量(Variable)</a></h1>
+<h1><a class="toc-backref" href="#id20">变量(Variable)</a></h1>
<p>是一个名字(name),是指向一个值(value)的名字。</p>
<p>值存放在内存(memory)中的某个地址。</p>
<p>尽量选有意义的简短的名字。比如,代表个数用n,代表索引用i,j,k。</p>
@@ -592,7 +599,7 @@ A list of objects</dd>
</ul>
</div>
<div class="section" id="mutable">
-<h1><a class="toc-backref" href="#id17">可变(mutable)类型与不可变类型</a></h1>
+<h1><a class="toc-backref" href="#id21">可变(mutable)类型与不可变类型</a></h1>
<p>字符串是不可变的(immutable)类型,不能在原内存地址改变。</p>
<p>a = 'hello' 不可以原地修改a[0] = 'H'。需要修改a的值时,需要对a进行重新赋值a = 'Hello'。</p>
<p>列表是可变(mutable)类型,能在原内存地址改变。</p>
@@ -617,7 +624,8 @@ A list of objects</dd>
</blockquote>
</div>
<div class="section" id="id5">
-<h1><a class="toc-backref" href="#id18">数与格式化显示</a></h1>
+<h1><a class="toc-backref" href="#id22">数与格式化显示</a></h1>
+<blockquote>
<div class="line-block">
<div class="line">x = 3.1415926</div>
</div>
@@ -661,9 +669,10 @@ A list of objects</dd>
<div class="line-block">
<div class="line">print('%f' % (x))</div>
</div>
+</blockquote>
</div>
<div class="section" id="strings">
-<h1><a class="toc-backref" href="#id19">字符串(Strings)</a></h1>
+<h1><a class="toc-backref" href="#id23">字符串(Strings)</a></h1>
<p>由字符组成。</p>
<div class="line-block">
<div class="line">fruit = 'banana!'</div>
@@ -719,7 +728,7 @@ A list of objects</dd>
<p>以上 <tt class="docutils literal"># [start,stop,step]</tt> 代表注释(comment),注释以 <tt class="docutils literal">#</tt> 号开头。</p>
</div>
<div class="section" id="concatenation">
-<h1><a class="toc-backref" href="#id20">字符串相加(concatenation)</a></h1>
+<h1><a class="toc-backref" href="#id24">字符串相加(concatenation)</a></h1>
<p>输出Jack, Kack, Lack, Mack, Nack, Ouack, Pack, and Quack</p>
<div class="line-block">
<div class="line">prefixes = 'JKLMNOPQ'</div>
@@ -738,7 +747,7 @@ A list of objects</dd>
</div>
</div>
<div class="section" id="slice">
-<h1><a class="toc-backref" href="#id21">子串(slice)</a></h1>
+<h1><a class="toc-backref" href="#id25">子串(slice)</a></h1>
<p>s[n:m],其中n或m可省略。
包括第n个字符,不包括第m个字符。(索引自0开始)</p>
<div class="line-block">
@@ -762,7 +771,7 @@ A list of objects</dd>
</div>
</div>
<div class="section" id="id6">
-<h1><a class="toc-backref" href="#id22">搜索字符串</a></h1>
+<h1><a class="toc-backref" href="#id26">搜索字符串</a></h1>
<div class="line-block">
<div class="line">def find(word, c):</div>
<div class="line-block">
@@ -788,7 +797,7 @@ A list of objects</dd>
<p>练习:用上面三参数的find来做。</p>
</div>
<div class="section" id="string">
-<h1><a class="toc-backref" href="#id23">String类(对象)方法</a></h1>
+<h1><a class="toc-backref" href="#id27">String类(对象)方法</a></h1>
<div class="line-block">
<div class="line">upper()</div>
<div class="line">lower()</div>
@@ -801,14 +810,14 @@ A list of objects</dd>
</div>
</div>
<div class="section" id="in">
-<h1><a class="toc-backref" href="#id24">in操作符</a></h1>
+<h1><a class="toc-backref" href="#id28">in操作符</a></h1>
<p>'a' in 'banana'
'seed' in 'banana'</p>
<p>练习:写出下面的函数,使得
in_both('apples', 'oranges')返回'aes'</p>
</div>
<div class="section" id="id7">
-<h1><a class="toc-backref" href="#id25">字符串比较</a></h1>
+<h1><a class="toc-backref" href="#id29">字符串比较</a></h1>
<p>字典序(alphabetical order)。大写字母排在小写字母前。</p>
<p>字符串之间可以有以下对比操作:</p>
<div class="line-block">
@@ -824,7 +833,7 @@ in_both('apples', 'oranges')返回'aes'</p>
<p>即兴定义函数,制造一个长度不小于4的密码。</p>
</div>
<div class="section" id="id8">
-<h1><a class="toc-backref" href="#id26">列表</a></h1>
+<h1><a class="toc-backref" href="#id30">列表</a></h1>
<p>语言的内置(built-in)类型。注意与String类比,index也是从0开始, in操作符, 求长度,获得字串,遍历操作类似。</p>
<blockquote>
<div class="line-block">
@@ -865,7 +874,7 @@ in_both('apples', 'oranges')返回'aes'</p>
<dd>return 2*x</dd>
</dl>
<p>list(map(f, [1,2]]))</p>
-<p>filter方法,从几个值中选择符合条件的几个值</p>
+<p>filter方法,从几个值中选择符合条件的几个值。</p>
<blockquote>
<div class="line-block">
<div class="line">def f(x):</div>
@@ -942,7 +951,7 @@ a与b是指向[1,2,3]的两个references。
error-prone(易错)</p>
</div>
<div class="section" id="id9">
-<h1><a class="toc-backref" href="#id27">列表作为参数</a></h1>
+<h1><a class="toc-backref" href="#id31">列表作为参数</a></h1>
<blockquote>
<div class="line-block">
<div class="line">def delete_head(t):</div>
@@ -958,7 +967,7 @@ error-prone(易错)</p>
</blockquote>
</div>
<div class="section" id="append">
-<h1><a class="toc-backref" href="#id28">注意区别 <tt class="docutils literal">append</tt> 与 <tt class="docutils literal">+</tt> 操作符</a></h1>
+<h1><a class="toc-backref" href="#id32">注意区别 <tt class="docutils literal">append</tt> 与 <tt class="docutils literal">+</tt> 操作符</a></h1>
<blockquote>
<div class="line-block">
<div class="line">t1 = [1, 2]</div>
@@ -985,18 +994,53 @@ error-prone(易错)</p>
</dl>
</blockquote>
<div class="section" id="tdd-test-driven-development">
-<h2><a class="toc-backref" href="#id29">TDD - Test-driven Development</a></h2>
+<h2><a class="toc-backref" href="#id33">TDD - Test-driven Development</a></h2>
<p>测试驱动开发。 My favourite。 刺激有挑战性。 帮助厘清需求。 帮助编写代码。</p>
-<p>推荐使用pytest。如何安装? 使用命令 <tt class="docutils literal">pip install pytest</tt></p>
+<p>推荐使用pytest。如何安装? 使用命令 <tt class="docutils literal">pip install pytest</tt>。</p>
+<p>在 <tt class="docutils literal">test_cases.py</tt> 写如下测试用例。然后在命令行运行: <tt class="docutils literal">python <span class="pre">-m</span> pytest test_cases.py</tt> 。</p>
+<pre class="code python literal-block">
+<span class="comment single"># Copyright (c) Hui Lan 2019</span>
+
+<span class="keyword namespace">import</span> <span class="name namespace">random</span>
+<span class="keyword namespace">import</span> <span class="name namespace">string</span>
+
+<span class="keyword">def</span> <span class="name function">make_password</span><span class="punctuation">(</span><span class="name">n</span><span class="punctuation">):</span>
+ <span class="literal string doc">'''
+ Return a string of length n consisting of a combination of
+ letters, digits and special characters. Note that each password
+ must have at least one lower case letter, one upper case letter,
+ one digit and one special charater. Return an empty string if n
+ is less than 4.
+ '''</span>
+
+ <span class="keyword">if</span> <span class="name">n</span> <span class="operator">&lt;</span> <span class="literal number integer">4</span><span class="punctuation">:</span>
+ <span class="keyword">return</span> <span class="literal string single">''</span>
+
+ <span class="name">password</span> <span class="operator">=</span> <span class="name">random</span><span class="operator">.</span><span class="name">choice</span><span class="punctuation">(</span><span class="name">string</span><span class="operator">.</span><span class="name">ascii_lowercase</span><span class="punctuation">)</span> <span class="operator">+</span> \
+ <span class="name">random</span><span class="operator">.</span><span class="name">choice</span><span class="punctuation">(</span><span class="name">string</span><span class="operator">.</span><span class="name">ascii_uppercase</span><span class="punctuation">)</span> <span class="operator">+</span> \
+ <span class="name">random</span><span class="operator">.</span><span class="name">choice</span><span class="punctuation">(</span><span class="name">string</span><span class="operator">.</span><span class="name">digits</span><span class="punctuation">)</span> <span class="operator">+</span> \
+ <span class="name">random</span><span class="operator">.</span><span class="name">choice</span><span class="punctuation">(</span><span class="name">string</span><span class="operator">.</span><span class="name">punctuation</span><span class="punctuation">)</span> <span class="operator">+</span> \
+ <span class="literal string single">''</span><span class="operator">.</span><span class="name">join</span><span class="punctuation">([</span><span class="name">random</span><span class="operator">.</span><span class="name">choice</span><span class="punctuation">(</span><span class="name">string</span><span class="operator">.</span><span class="name">ascii_letters</span> <span class="operator">+</span> <span class="name">string</span><span class="operator">.</span><span class="name">digits</span> <span class="operator">+</span> <span class="name">string</span><span class="operator">.</span><span class="name">punctuation</span><span class="punctuation">)</span> <span class="keyword">for</span> <span class="name">i</span> <span class="operator word">in</span> <span class="name builtin">range</span><span class="punctuation">(</span><span class="name">n</span><span class="operator">-</span><span class="literal number integer">4</span><span class="punctuation">)])</span>
+
+ <span class="keyword">return</span> <span class="literal string single">''</span><span class="operator">.</span><span class="name">join</span><span class="punctuation">(</span><span class="name">random</span><span class="operator">.</span><span class="name">sample</span><span class="punctuation">(</span><span class="name">password</span><span class="punctuation">,</span> <span class="name">n</span><span class="punctuation">))</span> <span class="comment single"># shuffle password then return</span>
+
+
+
+
+<span class="keyword">if</span> <span class="name variable magic">__name__</span> <span class="operator">==</span> <span class="literal string single">'__main__'</span><span class="punctuation">:</span>
+ <span class="keyword">for</span> <span class="name">n</span> <span class="operator word">in</span> <span class="name builtin">range</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">,</span><span class="literal number integer">20</span><span class="punctuation">):</span>
+ <span class="name">pwd</span> <span class="operator">=</span> <span class="name">make_password</span><span class="punctuation">(</span><span class="name">n</span><span class="punctuation">)</span>
+ <span class="keyword">print</span><span class="punctuation">(</span><span class="name">pwd</span><span class="punctuation">)</span>
+</pre>
</div>
<div class="section" id="id10">
-<h2><a class="toc-backref" href="#id30">计算复杂度</a></h2>
+<h2><a class="toc-backref" href="#id34">计算复杂度</a></h2>
<p>用Big O表述复杂度。O(n), O(n^2), O(n^3)。</p>
<p>密码实验回顾。</p>
</div>
</div>
<div class="section" id="dictionary">
-<h1><a class="toc-backref" href="#id31">字典(Dictionary)</a></h1>
+<h1><a class="toc-backref" href="#id35">字典(Dictionary)</a></h1>
<p>Mutable数据类型。</p>
<p>实际开发中超级有用。</p>
<blockquote>
@@ -1020,66 +1064,228 @@ error-prone(易错)</p>
<p>key-value pair (item)</p>
<p>item的顺序不可预测,不是按照创建时的顺序。</p>
<div class="section" id="incremental-development">
-<h2><a class="toc-backref" href="#id32">递增开发(Incremental Development)</a></h2>
+<h2><a class="toc-backref" href="#id36">递增开发(Incremental Development)</a></h2>
<p>每次完成一小点。从易到难。</p>
<p>练习:给定一个字符串,数出每个字母出现的频率。</p>
-<blockquote>
-<div class="line-block">
-<div class="line">def histogram(s):</div>
-<div class="line-block">
-<div class="line">''' Cannot pass any test cases. '''</div>
-<div class="line">pass</div>
-</div>
-</div>
-<div class="line-block">
-<div class="line">def histogram(s):</div>
-<div class="line-block">
-<div class="line">''' Can pass the test case in which s is an empty string. '''</div>
-<div class="line">d = {}</div>
-<div class="line">return d</div>
-</div>
-</div>
-<div class="line-block">
-<div class="line">def histogram(s):</div>
-<div class="line-block">
-<div class="line">''' Can pass the test cases in which all characters in s are unique. '''</div>
-<div class="line">d = {}</div>
-<div class="line">for c in s:</div>
-<div class="line-block">
-<div class="line">d[c] = 1</div>
-</div>
-<div class="line">return d</div>
-</div>
-</div>
-<div class="line-block">
-<div class="line">def histogram(s):</div>
-<div class="line-block">
-<div class="line">''' Can pass all test cases. '''</div>
-<div class="line">d = {}</div>
-<div class="line">for c in s:</div>
-<div class="line-block">
-<div class="line">if c not in d:</div>
-<div class="line-block">
-<div class="line">d[c] = 1</div>
-</div>
-<div class="line">else:</div>
-<div class="line-block">
-<div class="line">d[c] += 1</div>
-</div>
+<pre class="code python literal-block">
+<span class="keyword">def</span> <span class="name function">histogram</span><span class="punctuation">(</span><span class="name">s</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Cannot pass any test cases. '''</span>
+ <span class="keyword">pass</span>
+
+<span class="keyword">def</span> <span class="name function">histogram</span><span class="punctuation">(</span><span class="name">s</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Can pass the test case in which s is an empty string. '''</span>
+ <span class="name">d</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="keyword">return</span> <span class="name">d</span>
+
+<span class="keyword">def</span> <span class="name function">histogram</span><span class="punctuation">(</span><span class="name">s</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Can pass the test cases in which all characters in s are unique. '''</span>
+ <span class="name">d</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="keyword">for</span> <span class="name">c</span> <span class="operator word">in</span> <span class="name">s</span><span class="punctuation">:</span>
+ <span class="name">d</span><span class="punctuation">[</span><span class="name">c</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="literal number integer">1</span>
+ <span class="keyword">return</span> <span class="name">d</span>
+
+<span class="keyword">def</span> <span class="name function">histogram</span><span class="punctuation">(</span><span class="name">s</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Can pass all test cases. '''</span>
+ <span class="name">d</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="keyword">for</span> <span class="name">c</span> <span class="operator word">in</span> <span class="name">s</span><span class="punctuation">:</span>
+ <span class="keyword">if</span> <span class="name">c</span> <span class="operator word">not</span> <span class="operator word">in</span> <span class="name">d</span><span class="punctuation">:</span>
+ <span class="name">d</span><span class="punctuation">[</span><span class="name">c</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="literal number integer">1</span>
+ <span class="keyword">else</span><span class="punctuation">:</span>
+ <span class="name">d</span><span class="punctuation">[</span><span class="name">c</span><span class="punctuation">]</span> <span class="operator">+=</span> <span class="literal number integer">1</span>
+ <span class="keyword">return</span> <span class="name">d</span>
+
+
+<span class="name">h</span> <span class="operator">=</span> <span class="name">histogram</span><span class="punctuation">(</span><span class="literal string single">'good'</span><span class="punctuation">)</span>
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">h</span><span class="punctuation">)</span>
+</pre>
+<p>练习:给定一个字符串,数出每个单词出现的频率。</p>
+<p>练习:给定一个新闻文本,数出每个单词出现的频率。考虑以下方面,(1)只考虑字典里有的单词。(2)单词周围如有标点符号,要先移除。</p>
+<pre class="code python literal-block">
+<span class="comment single"># Copyright (C) 2019 Hui Lan</span>
+<span class="comment single"># The following line fixes SyntaxError: Non-UTF-8 code starting with ...</span>
+<span class="comment single"># coding=utf8</span>
+
+<span class="keyword">def</span> <span class="name function">file2lst</span><span class="punctuation">(</span><span class="name">fname</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Return a list where each element is a word from fname. '''</span>
+ <span class="name">L</span> <span class="operator">=</span> <span class="punctuation">[]</span>
+ <span class="name">f</span> <span class="operator">=</span> <span class="name builtin">open</span><span class="punctuation">(</span><span class="name">fname</span><span class="punctuation">)</span>
+ <span class="keyword">for</span> <span class="name">line</span> <span class="operator word">in</span> <span class="name">f</span><span class="punctuation">:</span>
+ <span class="name">line</span> <span class="operator">=</span> <span class="name">line</span><span class="operator">.</span><span class="name">strip</span><span class="punctuation">()</span>
+ <span class="name">lst</span> <span class="operator">=</span> <span class="name">line</span><span class="operator">.</span><span class="name">split</span><span class="punctuation">()</span>
+ <span class="keyword">for</span> <span class="name">x</span> <span class="operator word">in</span> <span class="name">lst</span><span class="punctuation">:</span>
+ <span class="name">L</span><span class="operator">.</span><span class="name">append</span><span class="punctuation">(</span><span class="name">x</span><span class="punctuation">)</span>
+ <span class="name">f</span><span class="operator">.</span><span class="name">close</span><span class="punctuation">()</span>
+ <span class="keyword">return</span> <span class="name">L</span>
+
+
+<span class="keyword">def</span> <span class="name function">lst2dict</span><span class="punctuation">(</span><span class="name">lst</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Return a dictionary given list lst. Each key is an element in the lst.
+ The value is always 1.'''</span>
+ <span class="name">d</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="keyword">for</span> <span class="name">w</span> <span class="operator word">in</span> <span class="name">lst</span><span class="punctuation">:</span>
+ <span class="name">d</span><span class="punctuation">[</span><span class="name">w</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="literal number integer">1</span>
+ <span class="keyword">return</span> <span class="name">d</span>
+
+
+<span class="keyword namespace">import</span> <span class="name namespace">string</span>
+<span class="keyword">def</span> <span class="name function">remove_punctuation</span><span class="punctuation">(</span><span class="name">s</span><span class="punctuation">):</span>
+ <span class="name">p</span> <span class="operator">=</span> <span class="literal string single">',.:’“”'</span> <span class="operator">+</span> <span class="name">string</span><span class="operator">.</span><span class="name">punctuation</span>
+ <span class="name">t</span> <span class="operator">=</span> <span class="literal string single">''</span>
+ <span class="keyword">for</span> <span class="name">c</span> <span class="operator word">in</span> <span class="name">s</span><span class="punctuation">:</span>
+ <span class="keyword">if</span> <span class="operator word">not</span> <span class="name">c</span> <span class="operator word">in</span> <span class="name">p</span><span class="punctuation">:</span>
+ <span class="name">t</span> <span class="operator">+=</span> <span class="name">c</span>
+ <span class="keyword">elif</span> <span class="name">c</span> <span class="operator">==</span> <span class="literal string single">'’'</span><span class="punctuation">:</span> <span class="comment single"># handle the case such as May’s</span>
+ <span class="keyword">return</span> <span class="name">t</span>
+ <span class="keyword">return</span> <span class="name">t</span>
+
+<span class="keyword">def</span> <span class="name function">word_frequency</span><span class="punctuation">(</span><span class="name">fname</span><span class="punctuation">,</span> <span class="name">english_dictionary</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Return a dictionary where each key is a word both in the file fname and in
+ the dictionary english_dictionary, and the corresponding value is the frequency
+ of that word.'''</span>
+ <span class="name">d</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="name">L</span> <span class="operator">=</span> <span class="name">file2lst</span><span class="punctuation">(</span><span class="name">fname</span><span class="punctuation">)</span>
+ <span class="keyword">for</span> <span class="name">x</span> <span class="operator word">in</span> <span class="name">L</span><span class="punctuation">:</span>
+ <span class="name">x</span> <span class="operator">=</span> <span class="name">remove_punctuation</span><span class="punctuation">(</span><span class="name">x</span><span class="operator">.</span><span class="name">lower</span><span class="punctuation">())</span>
+ <span class="keyword">if</span> <span class="name">x</span> <span class="operator word">in</span> <span class="name">english_dictionary</span><span class="punctuation">:</span>
+ <span class="keyword">if</span> <span class="operator word">not</span> <span class="name">x</span> <span class="operator word">in</span> <span class="name">d</span><span class="punctuation">:</span>
+ <span class="name">d</span><span class="punctuation">[</span><span class="name">x</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="literal number integer">1</span>
+ <span class="keyword">else</span><span class="punctuation">:</span>
+ <span class="name">d</span><span class="punctuation">[</span><span class="name">x</span><span class="punctuation">]</span> <span class="operator">+=</span> <span class="literal number integer">1</span>
+ <span class="keyword">return</span> <span class="name">d</span>
+
+
+<span class="keyword">def</span> <span class="name function">sort_by_value</span><span class="punctuation">(</span><span class="name">d</span><span class="punctuation">):</span>
+ <span class="literal string doc">''' Return a sorted list of tuples, each tuple containing a key and a value.
+ Note that the tuples are order in descending order of the value.'''</span>
+ <span class="keyword namespace">import</span> <span class="name namespace">operator</span>
+ <span class="name">lst</span> <span class="operator">=</span> <span class="name builtin">sorted</span><span class="punctuation">(</span><span class="name">d</span><span class="operator">.</span><span class="name">items</span><span class="punctuation">(),</span> <span class="name">key</span><span class="operator">=</span><span class="name">operator</span><span class="operator">.</span><span class="name">itemgetter</span><span class="punctuation">(</span><span class="literal number integer">1</span><span class="punctuation">),</span> <span class="name">reverse</span><span class="operator">=</span><span class="name builtin pseudo">True</span><span class="punctuation">)</span>
+ <span class="keyword">return</span> <span class="name">lst</span>
+
+
+<span class="keyword">if</span> <span class="name variable magic">__name__</span> <span class="operator">==</span> <span class="literal string single">'__main__'</span><span class="punctuation">:</span>
+ <span class="name">ed</span> <span class="operator">=</span> <span class="name">lst2dict</span><span class="punctuation">(</span><span class="name">file2lst</span><span class="punctuation">(</span><span class="literal string single">'words.txt'</span><span class="punctuation">))</span> <span class="comment single"># from http://greenteapress.com/thinkpython2/code/words.txt</span>
+ <span class="name">d</span> <span class="operator">=</span> <span class="name">word_frequency</span><span class="punctuation">(</span><span class="literal string single">'brexit-news.txt'</span><span class="punctuation">,</span> <span class="name">ed</span><span class="punctuation">)</span>
+ <span class="name">lst</span> <span class="operator">=</span> <span class="name">sort_by_value</span><span class="punctuation">(</span><span class="name">d</span><span class="punctuation">)</span>
+ <span class="keyword">for</span> <span class="name">x</span> <span class="operator word">in</span> <span class="name">lst</span><span class="punctuation">:</span>
+ <span class="keyword">print</span><span class="punctuation">(</span><span class="literal string single">'</span><span class="literal string interpol">%s</span><span class="literal string single"> (</span><span class="literal string interpol">%d</span><span class="literal string single">)'</span> <span class="operator">%</span> <span class="punctuation">(</span><span class="name">x</span><span class="punctuation">[</span><span class="literal number integer">0</span><span class="punctuation">],</span> <span class="name">x</span><span class="punctuation">[</span><span class="literal number integer">1</span><span class="punctuation">]))</span>
+</pre>
+</div>
+<div class="section" id="keyvalue">
+<h2><a class="toc-backref" href="#id37">key与value互换</a></h2>
+<p>注意到在原来的字典中一个value可能对应多个key的值。比如 <tt class="docutils literal">d = <span class="pre">{'a':1,</span> <span class="pre">'b':2,</span> <span class="pre">'c':2}</span></tt> 中,2就对应两个key,'b'与'c'。</p>
+<pre class="code python literal-block">
+<span class="keyword">def</span> <span class="name function">inverse_dictionary</span><span class="punctuation">(</span><span class="name">d</span><span class="punctuation">):</span>
+ <span class="name">d2</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="keyword">for</span> <span class="name">k</span> <span class="operator word">in</span> <span class="name">d</span><span class="punctuation">:</span>
+ <span class="name">v</span> <span class="operator">=</span> <span class="name">d</span><span class="punctuation">[</span><span class="name">k</span><span class="punctuation">]</span>
+ <span class="keyword">if</span> <span class="operator word">not</span> <span class="name">v</span> <span class="operator word">in</span> <span class="name">d2</span><span class="punctuation">:</span>
+ <span class="name">d2</span><span class="punctuation">[</span><span class="name">v</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="punctuation">[</span><span class="name">k</span><span class="punctuation">]</span>
+ <span class="keyword">else</span><span class="punctuation">:</span>
+ <span class="name">d2</span><span class="punctuation">[</span><span class="name">v</span><span class="punctuation">]</span><span class="operator">.</span><span class="name">append</span><span class="punctuation">(</span><span class="name">k</span><span class="punctuation">)</span>
+ <span class="keyword">return</span> <span class="name">d2</span>
+
+
+
+<span class="name">d</span> <span class="operator">=</span> <span class="punctuation">{</span><span class="literal string single">'a'</span><span class="punctuation">:</span><span class="literal number integer">1</span><span class="punctuation">,</span> <span class="literal string single">'b'</span><span class="punctuation">:</span><span class="literal number integer">2</span><span class="punctuation">,</span> <span class="literal string single">'c'</span><span class="punctuation">:</span><span class="literal number integer">2</span><span class="punctuation">}</span>
+<span class="name">d2</span> <span class="operator">=</span> <span class="name">inverse_dictionary</span><span class="punctuation">(</span><span class="name">d</span><span class="punctuation">)</span>
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">d2</span><span class="punctuation">)</span>
+</pre>
+<p>练习: 用 <tt class="docutils literal">inverse_dictionary</tt> 对上面 <tt class="docutils literal">d = <span class="pre">word_frequency('brexit-news.txt',</span> ed)</tt> 产生的 <tt class="docutils literal">d</tt> 进行转化。然后按照单词出现频率从高到低把所有单词都显示出来。每行显示一个频率内的所有单词。</p>
+<pre class="code python literal-block">
+<span class="name">d2</span> <span class="operator">=</span> <span class="name">inverse_dictionary</span><span class="punctuation">(</span><span class="name">d</span><span class="punctuation">)</span>
+<span class="keyword">for</span> <span class="name">k</span> <span class="operator word">in</span> <span class="name builtin">sorted</span><span class="punctuation">(</span><span class="name">d2</span><span class="operator">.</span><span class="name">keys</span><span class="punctuation">(),</span> <span class="name">reverse</span><span class="operator">=</span><span class="name builtin pseudo">True</span><span class="punctuation">):</span>
+ <span class="keyword">print</span><span class="punctuation">(</span><span class="literal string single">'</span><span class="literal string interpol">%d</span><span class="literal string single"> </span><span class="literal string interpol">%s</span><span class="literal string single">'</span> <span class="operator">%</span> <span class="punctuation">(</span><span class="name">k</span><span class="punctuation">,</span> <span class="literal string single">' '</span><span class="operator">.</span><span class="name">join</span><span class="punctuation">(</span><span class="name">d2</span><span class="punctuation">[</span><span class="name">k</span><span class="punctuation">])))</span>
+</pre>
+<p>练习: 使用 <tt class="docutils literal">setdefault</tt> 方法对上面的 <tt class="docutils literal">inverse_dictionary</tt> 进行简化 (减少行数)。</p>
+<pre class="code python literal-block">
+<span class="keyword">def</span> <span class="name function">inverse_dictionary</span><span class="punctuation">(</span><span class="name">d</span><span class="punctuation">):</span>
+ <span class="name">d2</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="keyword">for</span> <span class="name">k</span> <span class="operator word">in</span> <span class="name">d</span><span class="punctuation">:</span>
+ <span class="name">v</span> <span class="operator">=</span> <span class="name">d</span><span class="punctuation">[</span><span class="name">k</span><span class="punctuation">]</span>
+ <span class="name">d2</span><span class="operator">.</span><span class="name">setdefault</span><span class="punctuation">(</span><span class="name">v</span><span class="punctuation">,</span> <span class="punctuation">[])</span><span class="operator">.</span><span class="name">append</span><span class="punctuation">(</span><span class="name">k</span><span class="punctuation">)</span>
+
+ <span class="keyword">return</span> <span class="name">d2</span>
+</pre>
</div>
-<div class="line">return d</div>
</div>
+<div class="section" id="id11">
+<h1><a class="toc-backref" href="#id38">函数</a></h1>
+<p>函数 <tt class="docutils literal">unique_words</tt> 与 <tt class="docutils literal">unique_words2</tt> 哪个运行速度快?</p>
+<pre class="code python literal-block">
+<span class="keyword">def</span> <span class="name function">unique_words</span><span class="punctuation">(</span><span class="name">lst</span><span class="punctuation">):</span>
+ <span class="name">d</span> <span class="operator">=</span> <span class="punctuation">{}</span>
+ <span class="keyword">for</span> <span class="name">x</span> <span class="operator word">in</span> <span class="name">lst</span><span class="punctuation">:</span>
+ <span class="name">d</span><span class="punctuation">[</span><span class="name">x</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="literal number integer">1</span>
+ <span class="keyword">return</span> <span class="name builtin">sorted</span><span class="punctuation">(</span><span class="name">d</span><span class="operator">.</span><span class="name">keys</span><span class="punctuation">())</span>
+
+<span class="keyword">def</span> <span class="name function">unique_words2</span><span class="punctuation">(</span><span class="name">lst</span><span class="punctuation">):</span>
+ <span class="keyword">return</span> <span class="name builtin">sorted</span><span class="punctuation">(</span><span class="name builtin">list</span><span class="punctuation">(</span><span class="name builtin">set</span><span class="punctuation">(</span><span class="name">lst</span><span class="punctuation">)))</span>
+
+
+<span class="name">N</span> <span class="operator">=</span> <span class="literal number integer">10000000</span>
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">unique_words</span><span class="punctuation">([</span><span class="literal string single">'hello'</span><span class="punctuation">,</span> <span class="literal string single">'world'</span><span class="punctuation">,</span> <span class="literal string single">'am'</span><span class="punctuation">,</span> <span class="literal string single">'he'</span><span class="punctuation">]</span> <span class="operator">*</span> <span class="name">N</span><span class="punctuation">))</span>
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">unique_words2</span><span class="punctuation">([</span><span class="literal string single">'hello'</span><span class="punctuation">,</span> <span class="literal string single">'world'</span><span class="punctuation">,</span> <span class="literal string single">'am'</span><span class="punctuation">,</span> <span class="literal string single">'he'</span><span class="punctuation">]</span> <span class="operator">*</span> <span class="name">N</span><span class="punctuation">))</span>
+</pre>
+<div class="section" id="id12">
+<h2><a class="toc-backref" href="#id39">局部变量</a></h2>
+<p>在函数之内。函数执行结束,局部变量消失。</p>
</div>
-<div class="line-block">
-<div class="line">h = histogram('good')</div>
-<div class="line">print(h)</div>
+<div class="section" id="id13">
+<h2><a class="toc-backref" href="#id40">全局变量</a></h2>
+<p>全局变量位于函数之外,模块之内。全局变量对所有模块内的函数可见(可读)。如果在函数内要对全局变量重新赋值,那么要先用 <tt class="docutils literal">global</tt> 声明之 (declare)。</p>
+<pre class="code python literal-block">
+<span class="name">verbose</span> <span class="operator">=</span> <span class="name builtin pseudo">True</span>
+
+<span class="keyword">def</span> <span class="name function">example1</span><span class="punctuation">():</span>
+ <span class="keyword">if</span> <span class="name">verbose</span><span class="punctuation">:</span>
+ <span class="keyword">print</span><span class="punctuation">(</span><span class="literal string single">'Running example1'</span><span class="punctuation">)</span>
+
+<span class="keyword">def</span> <span class="name function">example2</span><span class="punctuation">():</span>
+ <span class="name">verbose</span> <span class="operator">=</span> <span class="name builtin pseudo">False</span> <span class="comment single"># a NEW local variable verbose</span>
+ <span class="keyword">if</span> <span class="name">verbose</span><span class="punctuation">:</span>
+ <span class="keyword">print</span><span class="punctuation">(</span><span class="literal string single">'Running example2'</span><span class="punctuation">)</span>
+
+<span class="keyword">def</span> <span class="name function">example3</span><span class="punctuation">():</span>
+ <span class="keyword">global</span> <span class="name">verbose</span> <span class="comment single"># I am actually going to use the global variable verbose; don't create a local one.</span>
+ <span class="name">verbose</span> <span class="operator">=</span> <span class="name builtin pseudo">False</span>
+ <span class="keyword">if</span> <span class="name">verbose</span><span class="punctuation">:</span>
+ <span class="keyword">print</span><span class="punctuation">(</span><span class="literal string single">'Running example3'</span><span class="punctuation">)</span>
+
+
+
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">verbose</span><span class="punctuation">)</span>
+<span class="name">example1</span><span class="punctuation">()</span>
+
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">verbose</span><span class="punctuation">)</span>
+<span class="name">example2</span><span class="punctuation">()</span>
+<span class="name">example1</span><span class="punctuation">()</span>
+
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">verbose</span><span class="punctuation">)</span>
+<span class="name">example3</span><span class="punctuation">()</span>
+<span class="name">example1</span><span class="punctuation">()</span>
+
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">verbose</span><span class="punctuation">)</span>
+</pre>
+<p>全局的列表与字典,如果只需改变其内容,而不是重新赋值,则不需要用 <tt class="docutils literal">global</tt> 声明。</p>
+<pre class="code python literal-block">
+<span class="name">record</span> <span class="operator">=</span> <span class="punctuation">{</span><span class="literal string single">'s1'</span><span class="punctuation">:</span><span class="literal number integer">65</span><span class="punctuation">,</span> <span class="literal string single">'s2'</span><span class="punctuation">:</span><span class="literal number integer">60</span><span class="punctuation">}</span>
+
+<span class="keyword">def</span> <span class="name function">add_score</span><span class="punctuation">(</span><span class="name">student</span><span class="punctuation">,</span> <span class="name">score</span><span class="punctuation">):</span>
+ <span class="name">record</span><span class="punctuation">[</span><span class="name">student</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="name">score</span>
+
+
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">record</span><span class="punctuation">)</span>
+<span class="name">add_score</span><span class="punctuation">(</span><span class="literal string single">'s3'</span><span class="punctuation">,</span> <span class="literal number integer">75</span><span class="punctuation">)</span>
+<span class="keyword">print</span><span class="punctuation">(</span><span class="name">record</span><span class="punctuation">)</span>
+</pre>
+<p>练习: 定义一个函数 <tt class="docutils literal">empty_dict</tt> 清空字典 <tt class="docutils literal">record</tt>。 要求: 不能用 <tt class="docutils literal">return</tt> 语句。 提示: 可以用 <tt class="docutils literal">pop</tt> 方法, 或者直接给 <tt class="docutils literal">record</tt> 赋值 <tt class="docutils literal">{}</tt> 。</p>
</div>
-</blockquote>
-<p>练习:给定一个字符串,数出每个单词出现的频率。</p>
+<div class="section" id="id14">
+<h2><a class="toc-backref" href="#id41">函数执行顺序</a></h2>
</div>
</div>
-<div class="section" id="id11">
-<h1><a class="toc-backref" href="#id33">参考</a></h1>
+<div class="section" id="id15">
+<h1><a class="toc-backref" href="#id42">参考</a></h1>
<ul class="simple">
<li>Think Python 2e – Green Tea Press. <a class="reference external" href="http://greenteapress.com/thinkpython2/thinkpython2.pdf">http://greenteapress.com/thinkpython2/thinkpython2.pdf</a>.</li>
</ul>