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border: 0px; +} +table.docutils.booktabs th { + border-bottom: thin solid; + text-align: left; +} + +h1 tt.docutils, h2 tt.docutils, h3 tt.docutils, +h4 tt.docutils, h5 tt.docutils, h6 tt.docutils { + font-size: 100% } + +ul.auto-toc { + list-style-type: none } + +</style> +</head> +<body> +<div class="document" id="lecture-notes-on-python"> +<h1 class="title">Lecture Notes on Python</h1> +<table class="docinfo" frame="void" rules="none"> +<col class="docinfo-name" /> +<col class="docinfo-content" /> +<tbody valign="top"> +<tr><th class="docinfo-name">Authors:</th> +<td>蓝珲 (lanhui AT zjnu.edu.cn)</td></tr> +<tr><th class="docinfo-name">Version:</th> +<td>0.1 of 2019/03/30</td></tr> +</tbody> +</table> +<p>非学究写书，无空洞行文。Python语法简洁，库函数全面强大，编程速度快，运行速度也不慢。</p> +<div class="section" id="python"> +<h1>Python的发音纠正</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&tf=U2VydmljZT1EaWN0aW9uYXJ5QW5zd2VyVjIgU2NlbmFyaW89RGVmaW5pdGlvblNjZW5hcmlvIFBvc2l0aW9uPU5PUCBSYW5raW5nRGF0YT1UcnVlIEZvcmNlUGxhY2U9RmFsc2UgUGFpcnM9RGljdGlvbmFyeVdvcmQ6cHl0aG9uO3NjbjpEZWZpbml0aW9uU2NlbmFyaW87cDpRQVM7IHw%3d&hs=hyRBF0mYq9hrfQUq66DIZnFVta1ZGRfBiBks25oUguk%3d">pronounciation</a></p> +</div> +<div class="section" id="id1"> +<h1>Python源流</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> +<p>Python语法简洁，有大而全而有用的标准库。</p> +<p>自然（natural）语言。特点：歧义，重复。“The penny dropped。” “不要。”</p> +<p>正式（formal）语言。特点：只管字面意思。</p> +<p>计算机组成概要：CPU，总线，内存，硬盘。</p> +<p>Bit, byte, KB, MB, GB, TB换算。</p> +<p>变量的命名。如，层叠策略，用CDCL还是TiledStrategy?</p> +<p>教务管理系统，<a class="reference external" href="http://10.1.70.164/jwglxt">http://10.1.70.164/jwglxt</a>?</p> +<p>习语言、易语言等目前非主流语言。</p> +<p>最简单的类定义:</p> +<blockquote> +<dl class="docutils"> +<dt>class A:</dt> +<dd>pass</dd> +</dl> +</blockquote> +<p>以上面的类为蓝本，创建一个实例：a = A()。 虽然这个a什么也做不了。</p> +<p>Python文件命令行执行。 python a.py。</p> +<p>函数头的三要素：def，函数名，参数列表:</p> +<blockquote> +<div class="line-block"> +<div class="line">def add_number(a, b):</div> +<div class="line-block"> +<div class="line">return a + b</div> +</div> +</div> +<div class="line-block"> +<div class="line">def add_lst(a, b):</div> +<div class="line-block"> +<div class="line">if len(a) != len(b):</div> +<div class="line-block"> +<div class="line">return 'ERROR: a and b not in equal length.'</div> +</div> +<div class="line">n = len(a)</div> +<div class="line">result = []</div> +<div class="line">for i in range(n):</div> +<div class="line-block"> +<div class="line">result.append(a[i] + b[i])</div> +</div> +<div class="line">return result</div> +<div class="line"><br /></div> +</div> +<div class="line">print( add_lst([1,2,3],[-1,-2,-3]) )</div> +</div> +</blockquote> +</div> +<div class="section" id="id2"> +<h1>Python的关键词</h1> +<div class="line-block"> +<div class="line">def pass</div> +<div class="line">from import</div> +<div class="line">False True</div> +<div class="line">in</div> +<div class="line">None</div> +<div class="line">class</div> +<div class="line">return</div> +<div class="line">while for</div> +<div class="line">continue break</div> +<div class="line">and or not</div> +<div class="line">if else elif</div> +<div class="line">try except finally raise</div> +<div class="line">lambda nonlocal</div> +<div class="line">del global with</div> +<div class="line">yield assert</div> +<div class="line">as is</div> +</div> +<p>关键词被语言留用（reserved），无法作变量名。</p> +</div> +<div class="section" id="id3"> +<h1>值的类型</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"> +<dt>字符串（string）。'hello', 100 * 'hello', 'hello' * 100, 'Weight is %4.2f kg' % (70.2)</dt> +<dd>f = open('a.html') +s = f.read() +f.close()</dd> +<dt>列表（list）。['a', 'b', 'c', 'd']</dt> +<dd>['bob', 170, 'john', '180'] +[1, 2, 3, 4] +range(10) 返回一个range对象。可以用list函数把这个对象变成列表。 +等价的是range(0, 10, 1)，从0开始，步进1，不包括10。 +A list of list +A list of tuples +A list of objects</dd> +</dl> +<p>元组（tuple），字典（dict）。</p> +</div> +<div class="section" id="variable"> +<h1>变量（Variable）</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> +<p>关键词不能用作变量名。</p> +<p>值存放在内存某处。值会记录指向它的变量个数。</p> +<p>为节省空间，如果几个变量的值相同，那么这些变量有时会指向这个值（而不是为每个变量单独分配内存空间单独存放该值）。</p> +<p>这叫做interning技术。但并非总是如此。</p> +<div class="line-block"> +<div class="line">a = 10</div> +<div class="line">b = 10</div> +<div class="line">c = 10</div> +<div class="line">id(a), id(b), id(c)</div> +<div class="line">(8791229060416, 8791229060416, 8791229060416)</div> +</div> +<p>值10存在地址8791229060416，所有a，b，c三个变量都指向（point to）这个地址。</p> +<div class="line-block"> +<div class="line">x = 257</div> +<div class="line">y = 257</div> +<div class="line">id(x), id(y)</div> +<div class="line">(46487024, 46487952)</div> +</div> +<p>以上虽然变量x与y的值都是一样，可是这两个值存放在不同的内存地址。</p> +<div class="line-block"> +<div class="line">s1 = 'hello'</div> +<div class="line">s2 = 'hello'</div> +<div class="line">id(s1), id(s2)</div> +<div class="line">s1 == s2</div> +<div class="line">s1 is s2</div> +</div> +<div class="line-block"> +<div class="line">s1 = 'h' * 100</div> +<div class="line">s2 = 'h' * 100</div> +<div class="line">id(s1), id(s2)</div> +</div> +<div class="line-block"> +<div class="line">s3 = 'hello, world!'</div> +<div class="line">s4 = 'hello, world!'</div> +<div class="line">id(s3), id(s4)</div> +<div class="line">(46703536, 46705136)</div> +</div> +<div class="line-block"> +<div class="line">class A:</div> +<div class="line-block"> +<div class="line">pass</div> +</div> +</div> +<div class="line-block"> +<div class="line">a = A()</div> +<div class="line">b = A()</div> +<div class="line">a</div> +<div class="line"><__main__.A object at 0x0000000002CD92E8></div> +<div class="line">b</div> +<div class="line"><__main__.A object at 0x0000000002CD9240></div> +</div> +<div class="line-block"> +<div class="line">x = [1,2,3]</div> +<div class="line">id(x)</div> +<div class="line">46869512</div> +<div class="line">y = x</div> +<div class="line">id(y)</div> +<div class="line">46869512</div> +<div class="line">x.append(4)</div> +<div class="line">x</div> +<div class="line">[1, 2, 3, 4]</div> +<div class="line">y</div> +<div class="line">[1, 2, 3, 4]</div> +</div> +<div class="line-block"> +<div class="line">x = []</div> +<div class="line">id(x)</div> +<div class="line">46869640</div> +</div> +<div class="line-block"> +<div class="line">x = [1,2,3,4]</div> +<div class="line">y = [1,2,3,4]</div> +<div class="line">id(x)</div> +<div class="line">46869768</div> +<div class="line">id(y)</div> +<div class="line">46868808</div> +</div> +<p>一个没有名字与之对应的值将会被清出内存。</p> +<p>参考资料：</p> +<ul class="simple"> +<li><a class="reference external" href="http://foobarnbaz.com/2012/07/08/understanding-python-variables/">http://foobarnbaz.com/2012/07/08/understanding-python-variables/</a></li> +<li><a class="reference external" href="https://stackoverflow.com/questions/19721002/is-a-variable-the-name-the-value-or-the-memory-location">https://stackoverflow.com/questions/19721002/is-a-variable-the-name-the-value-or-the-memory-location</a></li> +</ul> +</div> +<div class="section" id="mutable"> +<h1>可变（mutable）类型与不可变类型</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> +<p>a = [1, 2] 可以原地修改a[0] = 2</p> +<p>参考资料：</p> +<ul class="simple"> +<li><a class="reference external" href="https://stackoverflow.com/questions/8056130/immutable-vs-mutable-types">https://stackoverflow.com/questions/8056130/immutable-vs-mutable-types</a></li> +</ul> +<p>表达式（expression）：值，变量或操作符的组合。</p> +<blockquote> +<div class="line-block"> +<div class="line">17</div> +<div class="line">n + 2</div> +</div> +</blockquote> +<p>语句（statement）：能够制造一个变量或者显示信息的代码。</p> +<blockquote> +<div class="line-block"> +<div class="line">n = 17</div> +<div class="line">print(n)</div> +</div> +</blockquote> +</div> +<div class="section" id="id4"> +<h1>数</h1> +<div class="line-block"> +<div class="line">x = 3.1415926</div> +</div> +<div class="line-block"> +<div class="line">print('%4.0f' % (x))</div> +<div class="line">print('%4.1f' % (x))</div> +<div class="line">print('%4.2f' % (x))</div> +<div class="line">print('%4.3f' % (x))</div> +<div class="line">print('%4.4f' % (x))</div> +</div> +<div class="line-block"> +<div class="line">print('%6.0f' % (x))</div> +<div class="line">print('%6.1f' % (x))</div> +<div class="line">print('%6.2f' % (x))</div> +<div class="line">print('%6.3f' % (x))</div> +<div class="line">print('%6.4f' % (x))</div> +</div> +<div class="line-block"> +<div class="line">print('%.0f' % (x))</div> +<div class="line">print('%.1f' % (x))</div> +<div class="line">print('%.2f' % (x))</div> +<div class="line">print('%.3f' % (x))</div> +<div class="line">print('%.4f' % (x))</div> +<div class="line">print('%.5f' % (x))</div> +<div class="line">print('%.6f' % (x))</div> +<div class="line">print('%.7f' % (x))</div> +<div class="line">print('%.8f' % (x))</div> +<div class="line">print('%.9f' % (x))</div> +<div class="line">print('%.15f' % (x))</div> +<div class="line">print('%.16f' % (x))</div> +<div class="line">print('%.17f' % (x))</div> +<div class="line">print('%.18f' % (x))</div> +</div> +<div class="line-block"> +<div class="line">print('%4.f' % (x))</div> +<div class="line">print('%5.f' % (x))</div> +<div class="line">print('%6.f' % (x))</div> +<div class="line">print('%7.f' % (x))</div> +<div class="line">print('%8.f' % (x))</div> +</div> +<div class="line-block"> +<div class="line">print('%f' % (x))</div> +</div> +</div> +<div class="section" id="strings"> +<h1>字符串（Strings）</h1> +<p>由字符组成。</p> +<div class="line-block"> +<div class="line">fruit = 'banana!'</div> +<div class="line">first_letter = fruit[0]</div> +<div class="line">second_letter = fruit[1]</div> +</div> +<p>索引（index）从0开始，所以1代表第二个字符。只用整数。</p> +<p>负整数代表从字符串末尾开始。如fruit[-1]代表fruit字符串最后一个字符。</p> +<div class="line-block"> +<div class="line">i = 1</div> +<div class="line">fruit[i]</div> +<div class="line">fruit[i+1]</div> +</div> +<p>len()函数。返回字符串字符个数。len(fruit)。</p> +<div class="line-block"> +<div class="line">L = len(fruit)</div> +<div class="line">fruit[L-1]，最后一个字符。与fruit[-1]等价。</div> +</div> +<p>遍历（traverse）字符串。</p> +<blockquote> +<div class="line-block"> +<div class="line">fruit = 'banana'</div> +<div class="line">for c in fruit:</div> +<div class="line-block"> +<div class="line">print(c)</div> +</div> +</div> +</blockquote> +<p>反向遍历。</p> +<blockquote> +<div class="line-block"> +<div class="line">fruit = 'banana'</div> +<div class="line">for i in range(len(fruit)-1,-1,-1):</div> +<div class="line-block"> +<div class="line">print(fruit[i])</div> +</div> +</div> +<div class="line-block"> +<div class="line">fruit = 'banana'</div> +<div class="line">for c in fruit[::-1]: # [start,stop,step]</div> +<div class="line-block"> +<div class="line">print(c)</div> +</div> +</div> +<div class="line-block"> +<div class="line">fruit = 'banana'</div> +<div class="line">for c in ''.join(reversed(fruit)):</div> +<div class="line-block"> +<div class="line">print(c)</div> +</div> +</div> +</blockquote> +</div> +<div class="section" id="concatenation"> +<h1>字符串相加（concatenation）</h1> +<p>输出Jack, Kack, Lack, Mack, Nack, Ouack, Pack, and Quack</p> +<div class="line-block"> +<div class="line">prefixes = 'JKLMNOPQ'</div> +<div class="line">suffix = 'ack'</div> +<div class="line">for c in prefixes:</div> +<div class="line-block"> +<div class="line">if c == 'O' or c == 'Q':</div> +<div class="line-block"> +<div class="line">print(c + 'u' + suffix)</div> +</div> +<div class="line">else:</div> +<div class="line-block"> +<div class="line">print(c + suffix)</div> +</div> +</div> +</div> +</div> +<div class="section" id="slice"> +<h1>子串（slice）</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"> +<div class="line">s = 'Monty Python'</div> +<div class="line">s[0:5]</div> +<div class="line">s[6:12]</div> +<div class="line">s[:5]</div> +<div class="line">s[6:]</div> +<div class="line">s[:]</div> +</div> +<p>n一般小于m。如果n大于等于m，那么就返回空字符串。</p> +<p>空字符串的长度是0。</p> +<p>字符串是immutable的。不能改变已有的字符串。</p> +<div class="line-block"> +<div class="line">greeting = 'Hello, world!'</div> +<div class="line">greeting[0] = 'J'</div> +</div> +<div class="line-block"> +<div class="line">greeting = 'Hello, world!'</div> +<div class="line">new_greeting = 'J' + greeting[1:]</div> +</div> +</div> +<div class="section" id="id5"> +<h1>搜索字符串</h1> +<div class="line-block"> +<div class="line">def find(word, c):</div> +<div class="line-block"> +<div class="line">i = 0</div> +<div class="line">while i < len(word):</div> +<div class="line-block"> +<div class="line">if word[i] == c:</div> +<div class="line-block"> +<div class="line">return i</div> +</div> +<div class="line">i = i + 1</div> +</div> +<div class="line">return -1</div> +</div> +</div> +<div class="line-block"> +<div class="line">print(find('banana', 'a'))</div> +</div> +<p>练习一：加第三个参数，设定从哪个字符开始搜起。</p> +<p>练习二：加第三个参数，设定从哪个方向开始搜起。</p> +<p>String对象有内置函数find。</p> +<p>数字符串中某个字符的个数。</p> +<p>练习：用上面三参数的find来做。</p> +</div> +<div class="section" id="string"> +<h1>String类（对象）方法</h1> +<div class="line-block"> +<div class="line">upper()</div> +<div class="line">lower()</div> +</div> +<p>方法调用：invocation/call</p> +<div class="line-block"> +<div class="line">word.find('na')</div> +<div class="line">word.find('na', 3)</div> +<div class="line">name.find('b', 1, 2)</div> +</div> +</div> +<div class="section" id="in"> +<h1>in操作符</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="id6"> +<h1>字符串比较</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"> +<div class="line">==</div> +<div class="line">>, >=</div> +<div class="line"><, <=</div> +</div> +<p>练习：写is_reverse函数，使得is_reverse('god', 'dog')返回True。</p> +<p>find_from函数的两种实现。如果能够找出错误，给1分奖励。</p> +<p>字符串是对象（object）。</p> +<p>对象的本质涵义 - data construct。</p> +<p>计算复杂度。</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="id7"> +<h1>列表</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"> +<div class="line">[ ]</div> +<div class="line">[10, 20, 30, 40]</div> +<div class="line">['crunchy frog', 'ram bladder', 'lark vomit']</div> +</div> +</blockquote> +<p>列表中的元素不需要是同一类型的: <tt class="docutils literal">['spam', 2.0, 5, [10, 20]]</tt></p> +<p>列表[10,20]在另外一个列表中，这叫嵌套列表。</p> +<p>['spam', 1, ['Brie', 'Roquefort', 'Pol le Veq'], [1, 2, 3]]，长度是多少？</p> +<p>列表是 Mutable类型。值可以在原地变。（注意与String的区别）。</p> +<p>IndexError</p> +<p>遍历</p> +<dl class="docutils"> +<dt>for cheese in cheeses:</dt> +<dd>print(cheese)</dd> +<dt>for i in range(len(numbers)):</dt> +<dd>numbers[i] = numbers[i] * 2</dd> +<dt>for x in []:</dt> +<dd>print('This never happens.')</dd> +</dl> +<!-- 讨论软件工程认证数据输入问题。 --> +<p><tt class="docutils literal">+</tt> 操作符用来连接， <tt class="docutils literal">*</tt> 操作符用来重复。</p> +<p>列表的方法</p> +<p>append</p> +<p>extend</p> +<p>sort</p> +<p>t = ['d', 'c', 'e', 'b', 'a'] +t.sort() # 文t.sort()返回什么值？ +t</p> +<p>sum - reduce方法，把几个值变成一个值</p> +<p>map方法，把几个值变成另外几个值</p> +<dl class="docutils"> +<dt>def f(x):</dt> +<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> +<blockquote> +<div class="line-block"> +<div class="line">def f(x):</div> +<div class="line-block"> +<div class="line">if x % 2 == 0:</div> +<div class="line-block"> +<div class="line">return True</div> +</div> +<div class="line">return False</div> +</div> +</div> +<div class="line-block"> +<div class="line">list(filter(f, [1,2,3,4]))</div> +</div> +</blockquote> +<p>pop</p> +<p>t = ['a', 'b', 'c'] +x = t.pop(1) # pop可不带参数，不带参数返回哪个值？</p> +<p>t = ['a', 'b', 'c'] +del t[1]</p> +<p>t = ['a', 'b', 'c', 'd', 'e', 'f'] +del t[1:5]</p> +<p>t = ['a', 'b', 'c'] +t.remove('b')</p> +<p>list_of_characters = list('spam') +list_of_words = 'spam should be filtered'.split() +list_of_words = 'spam-should-be-filtered'.split('-')</p> +<p>join方法</p> +<p>','.join(['1','2','3'])</p> +<p>a = 'banana' +b = 'banana' +a is b # a与b是不是指向同一个值 +a == b</p> +<p>a = [1, 2, 3] +b = [1, 2, 3] +a is b # not identical, a and b are not the same object +a == b # equivalent though they have the same values</p> +<p>别名（Aliasing）</p> +<p>a = [1, 2, 3] +b = a +b is a</p> +<p>把变量名与对象联系起来叫做reference。 +a与b是指向[1,2,3]的两个references。 +因为[1,2,3]是mutable的，所以使用a对[1,2,3]做改变同样影响到b对应的值。 +error-prone（易错）</p> +</div> +<div class="section" id="id8"> +<h1>列表作为参数</h1> +<div class="line-block"> +<div class="line">def delete_head(t):</div> +<div class="line-block"> +<div class="line">del t[0]</div> +</div> +</div> +<div class="line-block"> +<div class="line">letters = ['a', 'b', 'c']</div> +<div class="line">delete_head(letters) # letters and t points to the same list object.</div> +<div class="line">letters</div> +</div> +</div> +<div class="section" id="append"> +<h1>注意区别 <tt class="docutils literal">append</tt> 与 <tt class="docutils literal">+</tt> 操作符</h1> +<p>t1 = [1, 2] +t2 = t1.append(3) +t1 +[1, 2, 3] +t2</p> +<p>t3 = t1 + [4] +t3 +[1, 2, 3, 4] +t1 +[1, 2, 3]</p> +<p>区别如下两个函数:</p> +<blockquote> +<dl class="docutils"> +<dt>def bad_delete_head(t):</dt> +<dd>t = t[1:] # WRONG!</dd> +<dt>def tail(t):</dt> +<dd>return t[1:]</dd> +</dl> +</blockquote> +</div> +<div class="section" id="dictionary"> +<h1>字典（Dictionary）</h1> +<p>Mutable</p> +<p>超级有用</p> +<div class="line-block"> +<div class="line">d = {} or d = dict()</div> +</div> +<div class="line-block"> +<div class="line">d = {'hot':'热', 'cool':'凉', 'cold':'冷'}</div> +<div class="line">d['warm'] = '温'</div> +<div class="line">d['warm']</div> +<div class="line">d['freezing'] # KeyError</div> +<div class="line">len(d)</div> +</div> +<div class="line-block"> +<div class="line">'warm' in d</div> +<div class="line">'温' in d.values()</div> +</div> +<p>key</p> +<p>value</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> +<p>练习：给定一个字符串，数出每个字母出现的频率。</p> +<p>练习：给定一个字符串，数出每个单词出现的频率。</p> +</div> +<div class="section" id="id9"> +<h1>参考</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> +<!-- Make a html page from this file. Issue the following command: +pip install docutils && rst2html.py LectureNotesOnPython.rst LectureNotesOnPython.html --> +</div> +</div> +</body> +</html> diff --git a/LectureNotesOnPython.rst b/LectureNotesOnPython.rst index af9d13d..ae28903 100644 --- a/LectureNotesOnPython.rst +++ b/LectureNotesOnPython.rst @@ -1,17 +1,484 @@ +======================= +Lecture Notes on Python +======================= + +:Authors: + 蓝珲 (lanhui AT zjnu.edu.cn) + +:Version: 0.1 of 2019/03/30 + + +非学究写书，无空洞行文。Python语法简洁，库函数全面强大，编程速度快，运行速度也不慢。 + + + +Python的发音纠正 +------------------------------ + +国人普遍把th发作s。 Not quite correct。 + +\ ˈpī-ˌthän , -thən\ pronounciation_ + +.. _pronounciation: https://cn.bing.com/search?q=define%20python&tf=U2VydmljZT1EaWN0aW9uYXJ5QW5zd2VyVjIgU2NlbmFyaW89RGVmaW5pdGlvblNjZW5hcmlvIFBvc2l0aW9uPU5PUCBSYW5raW5nRGF0YT1UcnVlIEZvcmNlUGxhY2U9RmFsc2UgUGFpcnM9RGljdGlvbmFyeVdvcmQ6cHl0aG9uO3NjbjpEZWZpbml0aW9uU2NlbmFyaW87cDpRQVM7IHw%3d&hs=hyRBF0mYq9hrfQUq66DIZnFVta1ZGRfBiBks25oUguk%3d + + + +Python源流 +------------------------------ + +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。 + +Python语法简洁，有大而全而有用的标准库。 + +自然（natural）语言。特点：歧义，重复。“The penny dropped。” “不要。” + +正式（formal）语言。特点：只管字面意思。 + +计算机组成概要：CPU，总线，内存，硬盘。 + +Bit, byte, KB, MB, GB, TB换算。 + +变量的命名。如，层叠策略，用CDCL还是TiledStrategy? + +教务管理系统，http://10.1.70.164/jwglxt? + +习语言、易语言等目前非主流语言。 + +最简单的类定义: + + + class A: + pass + + +以上面的类为蓝本，创建一个实例：a = A()。 虽然这个a什么也做不了。 + +Python文件命令行执行。 python a.py。 + +函数头的三要素：def，函数名，参数列表: + + + | def add_number(a, b): + | return a + b + + | def add_lst(a, b): + | if len(a) != len(b): + | return 'ERROR: a and b not in equal length.' + | n = len(a) + | result = [] + | for i in range(n): + | result.append(a[i] + b[i]) + | return result + | + | print( add_lst([1,2,3],[-1,-2,-3]) ) + + + + +Python的关键词 +-------------------------------- + + +| def pass +| from import +| False True +| in +| None +| class +| return +| while for +| continue break +| and or not +| if else elif +| try except finally raise +| lambda nonlocal +| del global with +| yield assert +| as is + + +关键词被语言留用（reserved），无法作变量名。 + + +值的类型 +------------------------- + +所有的值都是对象。a = 5, help(a) a.bit_length() + +数字。1， 1.，1.1， .1, 1e1, 1e-1, 1E1, 1E-1 + +字符串（string）。'hello', 100 * 'hello', 'hello' * 100, 'Weight is %4.2f kg' % (70.2) + f = open('a.html') + s = f.read() + f.close() + +列表（list）。['a', 'b', 'c', 'd'] + ['bob', 170, 'john', '180'] + [1, 2, 3, 4] + range(10) 返回一个range对象。可以用list函数把这个对象变成列表。 + 等价的是range(0, 10, 1)，从0开始，步进1，不包括10。 + A list of list + A list of tuples + A list of objects + +元组（tuple），字典（dict）。 + + + +变量（Variable） +------------------------------------ + +是一个名字（name），是指向一个值（value）的名字。 + +值存放在内存（memory）中的某个地址。 + +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。 + +关键词不能用作变量名。 + + +值存放在内存某处。值会记录指向它的变量个数。 + +为节省空间，如果几个变量的值相同，那么这些变量有时会指向这个值（而不是为每个变量单独分配内存空间单独存放该值）。 + +这叫做interning技术。但并非总是如此。 + + +| a = 10 +| b = 10 +| c = 10 +| id(a), id(b), id(c) +| (8791229060416, 8791229060416, 8791229060416) + + +值10存在地址8791229060416，所有a，b，c三个变量都指向（point to）这个地址。 + + + +| x = 257 +| y = 257 +| id(x), id(y) +| (46487024, 46487952) + + +以上虽然变量x与y的值都是一样，可是这两个值存放在不同的内存地址。 + + +| s1 = 'hello' +| s2 = 'hello' +| id(s1), id(s2) +| s1 == s2 +| s1 is s2 + +| s1 = 'h' * 100 +| s2 = 'h' * 100 +| id(s1), id(s2) + +| s3 = 'hello, world!' +| s4 = 'hello, world!' +| id(s3), id(s4) +| (46703536, 46705136) + + + +| class A: +| pass + +| a = A() +| b = A() +| a +| <__main__.A object at 0x0000000002CD92E8> +| b +| <__main__.A object at 0x0000000002CD9240> + + + +| x = [1,2,3] +| id(x) +| 46869512 +| y = x +| id(y) +| 46869512 +| x.append(4) +| x +| [1, 2, 3, 4] +| y +| [1, 2, 3, 4] + +| x = [] +| id(x) +| 46869640 + + +| x = [1,2,3,4] +| y = [1,2,3,4] +| id(x) +| 46869768 +| id(y) +| 46868808 + + +一个没有名字与之对应的值将会被清出内存。 + +参考资料： + +- http://foobarnbaz.com/2012/07/08/understanding-python-variables/ +- https://stackoverflow.com/questions/19721002/is-a-variable-the-name-the-value-or-the-memory-location + + + +可变（mutable）类型与不可变类型 +---------------------------------------------------------- + +字符串是不可变的（immutable）类型，不能在原内存地址改变。 + +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'。 + +列表是可变（mutable）类型，能在原内存地址改变。 + +a = [1, 2] 可以原地修改a[0] = 2 + +参考资料： + +- https://stackoverflow.com/questions/8056130/immutable-vs-mutable-types + + + +表达式（expression）：值，变量或操作符的组合。 + + | 17 + | n + 2 + +语句（statement）：能够制造一个变量或者显示信息的代码。 + + | n = 17 + | print(n) + + + + +数 +------ + +| x = 3.1415926 + +| print('%4.0f' % (x)) +| print('%4.1f' % (x)) +| print('%4.2f' % (x)) +| print('%4.3f' % (x)) +| print('%4.4f' % (x)) + + +| print('%6.0f' % (x)) +| print('%6.1f' % (x)) +| print('%6.2f' % (x)) +| print('%6.3f' % (x)) +| print('%6.4f' % (x)) + + +| print('%.0f' % (x)) +| print('%.1f' % (x)) +| print('%.2f' % (x)) +| print('%.3f' % (x)) +| print('%.4f' % (x)) +| print('%.5f' % (x)) +| print('%.6f' % (x)) +| print('%.7f' % (x)) +| print('%.8f' % (x)) +| print('%.9f' % (x)) +| print('%.15f' % (x)) +| print('%.16f' % (x)) +| print('%.17f' % (x)) +| print('%.18f' % (x)) + +| print('%4.f' % (x)) +| print('%5.f' % (x)) +| print('%6.f' % (x)) +| print('%7.f' % (x)) +| print('%8.f' % (x)) + +| print('%f' % (x)) + + + +字符串（Strings） +------------------------------------------ + +由字符组成。 + +| fruit = 'banana!' +| first_letter = fruit[0] +| second_letter = fruit[1] + +索引（index）从0开始，所以1代表第二个字符。只用整数。 + +负整数代表从字符串末尾开始。如fruit[-1]代表fruit字符串最后一个字符。 + +| i = 1 +| fruit[i] +| fruit[i+1] + +len()函数。返回字符串字符个数。len(fruit)。 + +| L = len(fruit) +| fruit[L-1]，最后一个字符。与fruit[-1]等价。 + + +遍历（traverse）字符串。 + + | fruit = 'banana' + | for c in fruit: + | print(c) + + +反向遍历。 + + | fruit = 'banana' + | for i in range(len(fruit)-1,-1,-1): + | print(fruit[i]) + + | fruit = 'banana' + | for c in fruit[::-1]: # [start,stop,step] + | print(c) + + + | fruit = 'banana' + | for c in ''.join(reversed(fruit)): + | print(c) + + + +字符串相加（concatenation） +------------------------------------------------------- + +输出Jack, Kack, Lack, Mack, Nack, Ouack, Pack, and Quack + +| prefixes = 'JKLMNOPQ' +| suffix = 'ack' +| for c in prefixes: +| if c == 'O' or c == 'Q': +| print(c + 'u' + suffix) +| else: +| print(c + suffix) + + +子串（slice） +------------------------------------------------------- + +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） + +| s = 'Monty Python' +| s[0:5] +| s[6:12] +| s[:5] +| s[6:] +| s[:] + +n一般小于m。如果n大于等于m，那么就返回空字符串。 + +空字符串的长度是0。 + +字符串是immutable的。不能改变已有的字符串。 + +| greeting = 'Hello, world!' +| greeting[0] = 'J' + +| greeting = 'Hello, world!' +| new_greeting = 'J' + greeting[1:] + + + +搜索字符串 +----------------------------- + +| def find(word, c): +| i = 0 +| while i < len(word): +| if word[i] == c: +| return i +| i = i + 1 +| return -1 + +| print(find('banana', 'a')) + +练习一：加第三个参数，设定从哪个字符开始搜起。 + +练习二：加第三个参数，设定从哪个方向开始搜起。 + +String对象有内置函数find。 + +数字符串中某个字符的个数。 + +练习：用上面三参数的find来做。 + + +String类（对象）方法 +------------------------------------------ + +| upper() +| lower() + +方法调用：invocation/call + +| word.find('na') +| word.find('na', 3) +| name.find('b', 1, 2) + + +in操作符 +------------------------------------------ + +'a' in 'banana' +'seed' in 'banana' + +练习：写出下面的函数，使得 +in_both('apples', 'oranges')返回'aes' + + +字符串比较 +------------------------------------------- + +字典序（alphabetical order）。大写字母排在小写字母前。 + + +字符串之间可以有以下对比操作: + +| == +| >, >= +| <, <= + + +练习：写is_reverse函数，使得is_reverse('god', 'dog')返回True。 + + + +find_from函数的两种实现。如果能够找出错误，给1分奖励。 + +字符串是对象（object）。 + +对象的本质涵义 - data construct。 + +计算复杂度。 + +即兴定义函数，制造一个长度不小于4的密码。 + + + 列表 ---- +-------------------- 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。 -`` -[] -[10, 20, 30, 40] -['crunchy frog', 'ram bladder', 'lark vomit'] -`` -列表中的元素不需要是同一类型的 + | [ ] + | [10, 20, 30, 40] + | ['crunchy frog', 'ram bladder', 'lark vomit'] + -['spam', 2.0, 5, [10, 20]] +列表中的元素不需要是同一类型的: ``['spam', 2.0, 5, [10, 20]]`` 列表[10,20]在另外一个列表中，这叫嵌套列表。 @@ -34,10 +501,11 @@ for i in range(len(numbers)): for x in []: print('This never happens.') -讨论软件工程认证数据输入问题。 + +.. 讨论软件工程认证数据输入问题。 -+操作符用来连接， *操作符用来重复 +``+`` 操作符用来连接， ``*`` 操作符用来重复。 列表的方法 @@ -64,12 +532,13 @@ list(map(f, [1,2]])) filter方法，从几个值中选择符合条件的几个值 -def f(x): - if x % 2 == 0: - return True - return False + | def f(x): + | if x % 2 == 0: + | return True + | return False + + | list(filter(f, [1,2,3,4])) -list(filter(f, [1,2,3,4])) pop @@ -120,19 +589,21 @@ a与b是指向[1,2,3]的两个references。 因为[1,2,3]是mutable的，所以使用a对[1,2,3]做改变同样影响到b对应的值。 error-prone（易错） + + 列表作为参数 ------------ +--------------------------------------------- -def delete_head(t): - del t[0] +| def delete_head(t): +| del t[0] -letters = ['a', 'b', 'c'] -delete_head(letters) # letters and t points to the same list object. -letters +| letters = ['a', 'b', 'c'] +| delete_head(letters) # letters and t points to the same list object. +| letters -注意区别append与+操作符 ---------------------- +注意区别 ``append`` 与 ``+`` 操作符 +---------------------------------------------- t1 = [1, 2] t2 = t1.append(3) @@ -149,43 +620,53 @@ t1 -区别如下两个函数 -def bad_delete_head(t): - t = t[1:] # WRONG! +区别如下两个函数: -def tail(t): - return t[1:] + def bad_delete_head(t): + t = t[1:] # WRONG! + + def tail(t): + return t[1:] + ---------------------------------- 字典（Dictionary） +--------------------------------- Mutable 超级有用 -d = {} or d = dict() - +| d = {} or d = dict() -d = {'hot':'热', 'cool':'凉', 'cold':'冷'} -d['warm'] = '温' -d['warm'] -d['freezing'] # KeyError -len(d) +| d = {'hot':'热', 'cool':'凉', 'cold':'冷'} +| d['warm'] = '温' +| d['warm'] +| d['freezing'] # KeyError +| len(d) -'warm' in d -'温' in d.values() +| 'warm' in d +| '温' in d.values() key + value + key-value pair (item) + item的顺序不可预测，不是按照创建时的顺序。 练习：给定一个字符串，数出每个字母出现的频率。 +练习：给定一个字符串，数出每个单词出现的频率。 + 参考 ------ - Think Python 2e – Green Tea Press. http://greenteapress.com/thinkpython2/thinkpython2.pdf. + + +.. Make a html page from this file. Issue the following command: + pip install docutils && rst2html.py LectureNotesOnPython.rst LectureNotesOnPython.html |