数值对象的构造(创建)函数

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          <h3 id="python">《Python 教程》授课笔记附件</h3>
<ul>
<li>讲师: 魏明择</li>
<li>时间: 2019</li>
</ul>
<h3 id="_1">数值对象的构造(创建)函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>float(obj)</td>
<td>用字符串或数字转换为浮点数, 如果不给出参数，则返回0.0</td>
</tr>
<tr>
<td>int(x, base=10)<br>int(x=0)</td>
<td>用数字或字符串转换为整数,如果不给出参数，则返回0</td>
</tr>
<tr>
<td>complex(r=0.0, i=0.0)</td>
<td>用数字创建一个复数(实部为r,虚部为i)</td>
</tr>
<tr>
<td>bool(x)</td>
<td>用x获取一个布尔值(True/False)</td>
</tr>
</tbody>
</table>
<h3 id="_2">预置(内建)的数值型函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>abs(x)</td>
<td>取x的绝对值</td>
</tr>
<tr>
<td>round(number[, ndigits])</td>
<td>对数值进行"四舍五入", ndigits是小数向右<br>取整的位数, 负数表示向左取整</td>
</tr>
<tr>
<td>pow(x, y, z=None)</td>
<td>相当于x ** y 或  x**y % z</td>
</tr>
</tbody>
</table>
<h3 id="help">help() 查看函数帮助：</h3>
<div class="codehilite"><pre>help函数
&gt;&gt;&gt; help(abs)  # 查看abs函数的帮助
</pre></div>

<h2 id="_3">基本输入输出</h2>
<h3 id="input">基本输入 input</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>input('提示字符串')</td>
<td>返回输入的字符串(仅Python3,'提示字符串' 可以是空)</td>
</tr>
</tbody>
</table>
<h3 id="print">基本输出函数 print</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)</td>
<td>将一系列的值以字符串形式输出到<br>标准输出设备上,默认为终端.</td>
</tr>
</tbody>
</table>
<h4 id="_4">参数选项</h4>
<div class="codehilite"><pre>选项的关键字参数为:
sep:   两个值之间的分隔符，默认为一个空格' '
end:   输出完毕后在流末尾自动追加一个字符串,默认为换行符'\n'
file:  流对象，默认为sys.stdout.
flush: 是否立即将流进行输出
</pre></div>

<h3 id="_5">字符编码转换函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>ord(c)</td>
<td>返回一个字符c的Unicode编码值</td>
</tr>
<tr>
<td>chr(i)</td>
<td>返回i这个值所对应的 字符</td>
</tr>
</tbody>
</table>
<h3 id="_6">整数转换为字符串函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>bin(i)</td>
<td>将整数转换为二进制字符串</td>
</tr>
<tr>
<td>oct(i)</td>
<td>将整数转换为八进制字符串</td>
</tr>
<tr>
<td>hex(i)</td>
<td>将整数转换为十六进制字符串</td>
</tr>
</tbody>
</table>
<h3 id="_7">字符串构造函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>str(obj='')</td>
<td>将对象转换为字符串</td>
</tr>
</tbody>
</table>
<h4 id="range">range()函数</h4>
<table>
<thead>
<tr>
<th>函数</th>
<th>意义</th>
</tr>
</thead>
<tbody>
<tr>
<td>range(stop)</td>
<td>用来生成 0 ~ stop 区间内的整数,直到stop为止（不包含stop)</td>
</tr>
<tr>
<td>range(start,stop[,step])</td>
<td>用来生成start~stop区间内的整数,直到stop为止,每个整数间隔step，直到stop为止（不包含stop，且step可以是负整数)</td>
</tr>
</tbody>
</table>
<h5 id="_8">格式:</h5>
<p>(见:help(range))</p>
<h3 id="list">列表的构造(创建)函数list</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>list()</td>
<td># 生成一个空的列表 等同于 []</td>
</tr>
<tr>
<td>list(iterable)</td>
<td># 用可迭代对象创建一个列表</td>
</tr>
</tbody>
</table>
<h3 id="python3">Python3中常用的序列函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>len(seq)</td>
<td>返回序列的长度</td>
</tr>
<tr>
<td>max(x)</td>
<td>返回序列的最大值的元素</td>
</tr>
<tr>
<td>min(x)</td>
<td>返回序列的最小值的元素</td>
</tr>
<tr>
<td>------以上是以前学的---------</td>
<td></td>
</tr>
<tr>
<td>sum(x)</td>
<td>返回序列中所有元素的和(元素必须是数值类型)</td>
</tr>
<tr>
<td>any(x)</td>
<td>真值测试，如果列表中其中一个值为真值则返回True</td>
</tr>
<tr>
<td>all(x)</td>
<td>真值测试，如果列表中所有值为真值则返回True</td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
<tr>
<td>reversed(seq)</td>
<td>返回原序列反向顺序的可迭代对象</td>
</tr>
<tr>
<td>sorted(iterable, reverse=False)</td>
<td>返回已排序对象的</td>
</tr>
<tr>
<td>str(obj)</td>
<td>将对象obj序列化为一个字符串</td>
</tr>
<tr>
<td>list(iterable)</td>
<td>用可迭代对象生成一个列表</td>
</tr>
<tr>
<td>tuple(iterable)</td>
<td>用可迭代对象生成一个元组</td>
</tr>
</tbody>
</table>
<h3 id="tuple">元组的构造(创建)函数tuple</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>tuple()</td>
<td>生成一个空的元组，等同于 ()</td>
</tr>
<tr>
<td>tuple(iterable)</td>
<td>用可迭代对象生成一个元组</td>
</tr>
</tbody>
</table>
<h4 id="dictdict">dict的构造(创建)函数dict</h4>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>dict()</td>
<td># 生成一个空的字典 等同于 {}</td>
</tr>
<tr>
<td>dict(iterable)</td>
<td>用可迭代对象初始化一个字典</td>
</tr>
<tr>
<td>dict(**kwargs)</td>
<td>关键字传参形式生成一个字典</td>
</tr>
</tbody>
</table>

<h3 id="set">集合构造(创建)函数 set</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>set()</td>
<td>创建一个空的集合对象(不能用{}来创建空集合)</td>
</tr>
<tr>
<td>set(iterable)</td>
<td>用可迭代对象创建一个新的集合对象</td>
</tr>
</tbody>
</table>
<h3 id="frozenset">固定集合构造(创建)函数 frozenset</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>frozenset()</td>
<td>创建一个空的固定集合对象</td>
</tr>
<tr>
<td>frozenset(iterable)</td>
<td>用可迭代对象创建一个新的固定集合对象</td>
</tr>
</tbody>
</table>
<h2 id="globals-locals">globals() / locals() 函数</h2>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>globals()</td>
<td>返回当前全局作用域内变量的字典</td>
</tr>
<tr>
<td>locals()</td>
<td>返回当前局部作用域内变量的字典</td>
</tr>
</tbody>
</table>
<h2 id="eval-exec">eval(), exec()  函数</h2>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>eval(source, globals=None, locals=None)</td>
<td>把一个字符串source当成一个表达式来执行，返回表达式执行后的结果</td>
</tr>
<tr>
<td>exec(source, globals=None, locals=None)</td>
<td>把一个字符串source当成程序来执行．</td>
</tr>
</tbody>
</table>

<h2 id="high-order-function">高阶函数 High Order Function</h2>
<table>
<thead>
<tr>
<th align="center">函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center">map(func, iterable, ...)</td>
<td>返回一个可迭代对象，此可迭代对象用<br>函数func对可迭代对象iterables中的每一个元素作为参数计算后得到结果;<br>当最短的一个可迭代对象不再提供数据时此可迭代对象生成结束</td>
</tr>
<tr>
<td align="center">filter(function, iterable)</td>
<td>返回一个可迭代器对象，此可迭代对象将对iterabler获取到的数据<br>用函数function 进行筛选.function将对iterable中的每个元素进行求值，<br>返回False则将此数据丢弃，返回True，则保留此数据</td>
</tr>
<tr>
<td align="center">sorted(iterable,<br>key=None,<br>reverse=False)</td>
<td>返回一个新的包含有所有可迭代对象中数据升序排序的列表<br>iterable 可迭代对象<br>key 函数是用来提供一个值,这个值将作为排序的依据<br>reverse 标志用来设置是否降序排序</td>
</tr>
</tbody>
</table>
<h3 id="dir">dir函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>dir([对象])</td>
<td>返回一个字符串列表</td>
</tr>
</tbody>
</table>
<h4 id="dir_1">dir函数作用</h4>
<ul>
<li>如果没有参数调用，则返回当前作用域内的所有变量的列表</li>
<li>如果给定一个对象作为参数，则返回这个对象的所有变量的列表<ul>
<li>对于一个模块,返回这个模块的全部变量</li>
<li>对于一个类对象，返回类对象的所有变量，并递归的基类对象的所有变量</li>
<li>对于其它对象返回所有变量、类变量和基类变量</li>
</ul>
</li>
</ul>
<h3 id="iternext">迭代器函数iter和next</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>iter(iterable)</td>
<td>从可迭代对象中返回一个迭代器,iterable必须是能提供一个迭代器的对象</td>
</tr>
<tr>
<td>next(iterator)</td>
<td>从迭代器iterator中获取下一个记录，如果无法获取一下条记录，则触发 StopIteration 异常</td>
</tr>
</tbody>
</table>
<h3 id="_9">迭代工具函数</h3>
<ul>
<li>迭代工具函数的作用是生成一个个性化可迭代对象</li>
</ul>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>zip(iter1 [,iter2 [...]])</td>
<td>返回一个zip生成器对象, 此对象用于生成一个元组，此元组的数据分别来自于参数中每个可迭代对象,生成元组的个数由最小的可迭代对象大小决定</td>
</tr>
<tr>
<td>enumerate(iterable, start=0)</td>
<td>返回一个enumerate生成器对象，此对象生成类型为(索引,值对)的元组,<br>默认索引从零开始，也可以用start指定</td>
</tr>
</tbody>
</table>
<h3 id="bytes">字节串的构造函数bytes</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>bytes()</td>
<td># 生成一个空的字节串 等同于 b''</td>
</tr>
<tr>
<td>bytes(整型可迭代对象)</td>
<td># 用可迭代对象初始化一个字节串</td>
</tr>
<tr>
<td>bytes(整数n)</td>
<td>生成n个值为0的字节串</td>
</tr>
<tr>
<td>bytes(字符串, encoding='utf-8')</td>
<td>用字符串的转换编码生成一个字节串</td>
</tr>
</tbody>
</table>
<h3 id="bytearray">字节数组的构造函数 bytearray</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>bytearray()</td>
<td>创建空的字节数组</td>
</tr>
<tr>
<td>bytearray(整数)</td>
<td>用可迭代对象初始化一个字节数组</td>
</tr>
<tr>
<td>bytearray(整型可迭代对象)</td>
<td>生成n个值为0的字节数组</td>
</tr>
<tr>
<td>bytearray(字符串, encoding='utf-8')</td>
<td>用字符串的转换编码生成一个字节数组</td>
</tr>
</tbody>
</table>
<h3 id="_10">文件的打开函数</h3>
<table>
<thead>
<tr>
<th>字符</th>
<th>含义</th>
</tr>
</thead>
<tbody>
<tr>
<td>open(file, mode='rt')</td>
<td>用于打开一个文件，返回此文件流对象. <br>如果打开文件失败，则会触发OSError 错误!   <br>如果要打开的文件不存在，则会触发FileNotFoundError 错误!</td>
</tr>
</tbody>
</table>
<h3 id="_11">用于类的函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>isinstance(obj, class_or_tuple)</td>
<td>返回这个对象obj 是否是 某个类的对象,或者某些类<br>中的一个类的对象,如果是返回True,否则返回False</td>
</tr>
<tr>
<td>type(obj)</td>
<td>返回对象的类型</td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<h3 id="super">super函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>super(cls, obj)</td>
<td>返回绑定超类的实例(要求obj必须为cls类型的实例)</td>
</tr>
<tr>
<td>super()</td>
<td>返回绑定超类的实例,等同于:super(<strong>class</strong>, 实例方法的第一个参数)，必须用在方法内调用</td>
</tr>
</tbody>
</table>
<h3 id="_12">用于类的函数</h3>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>issubclass(cls, class_or_tuple)</td>
<td>判断一个类是否继承自其它的类,如果此类cls是class 或 tuple中的一个派生子类则返回True,否则返回False</td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<h4 id="_13">对象的属性管理函数</h4>
<table>
<thead>
<tr>
<th>函数</th>
<th>说明</th>
</tr>
</thead>
<tbody>
<tr>
<td>getattr(obj, name[, default])</td>
<td>从一个对象得到对象的属性；getattr(x, 'y') 等同于x.y; 当属性不存在时,如果给<br>出default参数,则返回default,如果没有给出default 则产生一个AttributeError错误</td>
</tr>
<tr>
<td>hasattr(obj, name)</td>
<td>用给定的name返回对象obj是否有此属性,此种做法可以避免在getattr(obj, name)时引发错误</td>
</tr>
<tr>
<td>setattr(obj, name, value)</td>
<td>给对象obj的名为name的属性设置相应的值value, setattr(x, 'y', v) 等同于 x.y = v</td>
</tr>
<tr>
<td>delattr(obj, name)</td>
<td>删除对象obj中的name属性, delattr(x, 'y') 等同于 del x.y</td>
</tr>
</tbody>
</table>
<h4 id="_14">对象的属性管理函数示例:</h4>
<div class="codehilite"><pre>class Dog:
    pass
d = Dog()
d.color = '白色'
v = getattr(d, 'color')   # 等同于 v = d.color
v = getattr(d, 'kinds')  # 出错,没有d.kinds属性
v = getattr(d, 'kinds', '没有这个属性')  # v= '没有这个属性'
hasattr(d, 'color')  # True
hasattr(d, 'kinds')  # False
setattr(d, 'kinds', '京巴')  # 等同于d.kinds ='京巴'
hasattr(d, 'kinds')  # True
delattr(d, 'kinds')  # 等同于 del d.kinds
hasattr(d, 'kinds')  # False
</pre></div>
        </article>
      </div>
    </div>

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