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<h1>python语法总结</h1>
<div class="read-more clearfix">
<span class="date">2017/1/13 14:51 下午</span>
<span>posted in </span>
<span class="posted-in"><a href='python.html'>python</a></span>
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<div class="article-content">
<h2 id="toc_0">变量</h2>
<h3 id="toc_1">命令规则</h3>
<ul>
<li>必须是大小写英文,数字和_的组合,且不能用数字开头</li>
<li>不用声明,直接使用(同PHP)</li>
</ul>
<h3 id="toc_2">类型</h3>
<ul>
<li>整数</li>
<li>浮点</li>
<li>字符串</li>
<li>布尔</li>
<li>空: None (与0不同)</li>
<li>Tuple : 元组,值不可变更</li>
<li>List : 表,值可以变更[下限:上限:步长]</li>
<li>Dictionary : 字典</li>
<li>自定义数据类型</li>
</ul>
<h2 id="toc_3">语法</h2>
<h3 id="toc_4">缩进</h3>
<p>python强制使用缩进来解析块代码.</p>
<h3 id="toc_5">运算符</h3>
<ul>
<li>数学 : <code>+,-,*,/,**,%</code></li>
<li>判断 : <code>==,!=,>,>=,<,<=,in</code></li>
<li>逻辑 : <code>and,or,not</code></li>
</ul>
<h3 id="toc_6">条件语句</h3>
<pre><code class="language-python">if condition1:
do1
elif condition2:
do2
elif condition3:
do3
else:
do4
</code></pre>
<h3 id="toc_7">循环</h3>
<p><strong>for</strong></p>
<pre><code class="language-python">for elemnt in list:
statment
</code></pre>
<p><strong>while</strong></p>
<pre><code class="language-python">while condition:
statement
</code></pre>
<p><strong>continue</strong><br/>
<strong>break</strong></p>
<span id="more"></span><!-- more -->
<h3 id="toc_8">错误处理</h3>
<ul>
<li>函数返回值</li>
<li>异常处理</li>
</ul>
<pre><code class="language-python">try:
do1
except exception1:
do e1==只有exception1才会进入这里==
except exception2:
do e2
except:
do default e==默认的exception处理==
else:
do elsedo==如果没有exception则进入这里==
finally:
do finallydo==不论有没有发生exception都要执行==
</code></pre>
<h2 id="toc_9">函数</h2>
<h3 id="toc_10">定义函数</h3>
<p><strong>实现功能,重复利用</strong></p>
<pre><code class="language-python">def func_name(a,b,...):
statement
return v1,v2,...
</code></pre>
<p><strong>若没有return或者return后无返回值时,函数将自动返回None</strong></p>
<h3 id="toc_11">参数传递</h3>
<ul>
<li>按顺序传递</li>
<li>关键字传递</li>
<li>参数默认值</li>
<li>包裹传递(packing) & 解包裹(unpacking)</li>
</ul>
<p><strong>可混用,混用原则:</strong><em>先位置,后关键字,包裹位置,包裹关键字</em></p>
<h4 id="toc_12">packing</h4>
<pre><code class="language-python">>>> def pack(*param):
... print param
>>> pack(1,2,3,4,"abc")
(1, 2, 3, 4, 'abc')
</code></pre>
<p>平常应用,可以强制将tuple转换成list:</p>
<pre><code class="language-python">>>> def pack2(*param):
... param = list(param)
... param[0] = "Hello"
... param[1] = "Python"
... print param
>>> pack2(1,2,"end")
['Hello', 'Python', 'end']
</code></pre>
<h4 id="toc_13">unpacking</h4>
<p><code>**param</code></p>
<h3 id="toc_14">函数对象(lambda)</h3>
<blockquote>
<p>这种能够接受一个函数作为参数的函数叫做「高阶函数」（higher-order function），是来自函数式编程（functional programming）的思想。</p>
</blockquote>
<pre><code class="language-python">>>> seq=[1,2,3,4,5]
>>> map(lambda x:x**3, [ x for x in seq ])
[1, 8, 27, 64, 125]
</code></pre>
<p><strong>高阶函数</strong>:<br/>
* filter(function, sequence)：对sequence中的item依次执行function(item)，将执行结果为True的item组成一个List/String/Tuple（取决于sequence的类型）返回<br/>
* map(function, sequence) ：对sequence中的item依次执行function(item)，见执行结果组成一个List返回<br/>
* reduce(function, sequence, starting_value)：对sequence中的item顺序迭代调用function，如果有starting_value，还可以作为初始值调用，例如可以用来对List求和<br/>
* lambda：这是Python支持一种有趣的语法，它允许你快速定义单行的最小函数，类似与C语言中的宏，这些叫做lambda的函数，是从LISP借用来的，可以用在任何需要函数的地方</p>
<p><strong>lambda与def的差别</strong></p>
<pre><code class="language-python">map( lambda x: x*x, [y for y in range(10)] )
</code></pre>
<pre><code class="language-python">def sq(x):
return x * x
map(sq, [y for y in range(10)])
</code></pre>
<h2 id="toc_15">面向对象的类</h2>
<h3 id="toc_16">定义</h3>
<p><strong>使用class关键字定义一个类,并且类名首字母大写.</strong></p>
<h3 id="toc_17">语法</h3>
<pre><code class="language-python">class PyClass:
variables
functions
</code></pre>
<h3 id="toc_18">创建对象</h3>
<p><code>myClass = PyClass()</code></p>
<h3 id="toc_19">引用对象属性</h3>
<p><code>myClass.attribute</code></p>
<h3 id="toc_20">作用域</h3>
<ul>
<li>通过self调用类属性</li>
<li>对象生成时自动执行的特殊方法: <code>__init__()</code></li>
<li>类的属性是对数据的封装,方法则是对类的行为封装</li>
<li>类属性:
<ol>
<li>公有属性.</li>
<li>内置属性:由系统在定义类的时候默认添加,由前后两个下划线构成<code>__dict__</code>,<code>__module__</code></li>
<li>私有属性:不能被类以外的函数调用.定义时在属性名前加<code>__</code> </li>
</ol></li>
<li>方法也分为<strong>公有方法</strong>和<strong>私有方法</strong>
<ol>
<li>私有方法:以<code>__</code>定义</li>
<li>类方法:被<code>classmethod()</code>函数处理过的函数,添加类装饰器<code>@classmethod</code></li>
<li>静态方法:等于"全局函数"</li>
</ol></li>
</ul>
<pre><code class="language-python">from functools import wraps
class A:
# Decorator as an instance method
def decorator1(self, func):
@wraps(func)
def wrapper(*args, **kwargs):
print('Decorator 1')
return func(*args, **kwargs)
return wrapper
# Decorator as a class method
@classmethod
def decorator2(cls, func):
@wraps(func)
def wrapper(*args, **kwargs):
print('Decorator 2')
return func(*args, **kwargs)
return wrapper
</code></pre>
<h2 id="toc_21">模块</h2>
<h3 id="toc_22">模块导入</h3>
<pre><code class="language-python">import mod_name #引入模块
import m as k #引入后重命名
from m import func1 #引入m模块的func1方法
from m import * #从m中引入所有对象
</code></pre>
<h3 id="toc_23">模块调用</h3>
<p>mod.obj</p>
<h3 id="toc_24">模块搜索路径</h3>
<ol>
<li>程序所在目录</li>
<li>标准库的安装路径</li>
<li>操作系统环境变量PYTHONPATH的路径</li>
</ol>
<h3 id="toc_25">构建模块</h3>
<h3 id="toc_26">常用标准库</h3>
<ul>
<li>正则<code>re</code></li>
<li>时间与日期<code>time</code> <code>datetime</code></li>
<li>路径与文件<code>os.path</code> <code>glob</code></li>
<li>文件管理 <code>os</code> <code>shutil</code></li>
<li>存储对象 <code>pickle</code> <code>cPickle</code></li>
<li>子进程 <code>subprocess</code></li>
<li>信号 <code>signal</code></li>
<li>线程同步 <code>threading</code></li>
<li>进程信息 <code>os</code></li>
<li>多进程 <code>multiprocessing</code></li>
<li>数学 <code>math</code></li>
<li>随机数 <code>random</code></li>
<li>循环器 <code>itertools</code></li>
<li>数据库 <code>sqlite3</code></li>
<li><a href="https://docs.python.org/2/library">python2 more library</a></li>
</ul>
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