Python菜鸟之路：Python基础（三）

一、编码

　　推荐阅读《字符编码的前世今生》：http://tgideas.qq.com/webplat/info/news_version3/804/808/811/m579/201307/218730.shtml

1. 常见编码介绍

• GB2312编码：适用于汉字处理、汉字通信等系统之间的信息交换
• GBK编码：是汉字编码标准之一，是在 GB2312-80 标准基础上的内码扩展规范，使用了双字节编码，即每个汉子占2byte。
• ASCII编码：是对英语字符和二进制之间的关系做的统一规定
• Unicode编码：这是一种世界上所有字符的编码。当然了它没有规定的存储方式。
• UTF-8编码：是 Unicode Transformation Format - 8 bit 的缩写， UTF-8 是 Unicode 的一种实现方式。它是可变长的编码方式，可以使用 1~4 个字节表示一个字符，可根据不同的符号而变化字节长度。每个汉子占3byte。

2. 编码转换

　　Python内部的字符串一般都是 Unicode编码。代码中字符串的默认编码与代码文件本身的编码是一致的。所以要做一些编码转换通常是要以Unicode作为中间编码进行转换的，即先将其他编码的字符串解码（decode）成 Unicode，再从 Unicode编码（encode）成另一种编码。

• decode 的作用是将其他编码的字符串转换成 Unicode 编码，eg name.decode(“GB2312”)，表示将GB2312编码的字符串name转换成Unicode编码
• encode 的作用是将Unicode编码转换成其他编码的字符串，eg name.encode(”GB2312“)，表示将GB2312编码的字符串name转换成GB2312编码

　　所以在进行编码转换的时候必须先知道 name 是那种编码，然后 decode 成 Unicode 编码，最后才 encode 成需要编码的编码。当然了，如果 name 已经就是 Unicode 编码了，那么就不需要进行 decode 进行解码转换了，直接用 encode 就可以编码成你所需要的编码。值得注意的是：对 Unicode 进行编码和对 str 进行编码都是错误的。

　　要在同一个文本中进行两种编码的输出等操作就必须进行编码的转换，先用decode将文本原来的编码转换成Unicode，再用encode将编码转换成需要转换成的编码。

二、Set集合

　　Set集合是一个无序不重复的。源码中对他的诸多方法进行了说明

class set(object):
    """
    set() -> new empty set object
    set(iterable) -> new set object
    
    Build an unordered collection of unique elements.
    """
    def add(self, *args, **kwargs): # real signature unknown
        """
        Add an element to a set.
        
        This has no effect if the element is already present.
        """
        pass

    def clear(self, *args, **kwargs): # real signature unknown
        """ Remove all elements from this set. """
        pass

    def copy(self, *args, **kwargs): # real signature unknown
        """ Return a shallow copy of a set. """
        pass

    def difference(self, *args, **kwargs): # real signature unknown
        """
        Return the difference of two or more sets as a new set.
        
        (i.e. all elements that are in this set but not the others.)
        """
        pass

    def difference_update(self, *args, **kwargs): # real signature unknown
        """ Remove all elements of another set from this set. """
        pass

    def discard(self, *args, **kwargs): # real signature unknown
        """
        Remove an element from a set if it is a member.
        
        If the element is not a member, do nothing.
        """
        pass

    def intersection(self, *args, **kwargs): # real signature unknown
        """
        Return the intersection of two sets as a new set.
        
        (i.e. all elements that are in both sets.)
        """
        pass

    def intersection_update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the intersection of itself and another. """
        pass

    def isdisjoint(self, *args, **kwargs): # real signature unknown
        """ Return True if two sets have a null intersection. """
        pass

    def issubset(self, *args, **kwargs): # real signature unknown
        """ Report whether another set contains this set. """
        pass

    def issuperset(self, *args, **kwargs): # real signature unknown
        """ Report whether this set contains another set. """
        pass

    def pop(self, *args, **kwargs): # real signature unknown
        """
        Remove and return an arbitrary set element.
        Raises KeyError if the set is empty.
        """
        pass

    def remove(self, *args, **kwargs): # real signature unknown
        """
        Remove an element from a set; it must be a member.
        
        If the element is not a member, raise a KeyError.
        """
        pass

    def symmetric_difference(self, *args, **kwargs): # real signature unknown
        """
        Return the symmetric difference of two sets as a new set.
        
        (i.e. all elements that are in exactly one of the sets.)
        """
        pass

    def symmetric_difference_update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the symmetric difference of itself and another. """
        pass

    def union(self, *args, **kwargs): # real signature unknown
        """
        Return the union of sets as a new set.
        
        (i.e. all elements that are in either set.)
        """
        pass

    def update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the union of itself and others. """
        pass

    def __and__(self, *args, **kwargs): # real signature unknown
        """ Return self&value. """
        pass

    def __contains__(self, y): # real signature unknown; restored from __doc__
        """ x.__contains__(y) <==> y in x. """
        pass

    def __eq__(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass

    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def __ge__(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def __gt__(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        pass

    def __iand__(self, *args, **kwargs): # real signature unknown
        """ Return self&=value. """
        pass

    def __init__(self, seq=()): # known special case of set.__init__
        """
        set() -> new empty set object
        set(iterable) -> new set object
        
        Build an unordered collection of unique elements.
        # (copied from class doc)
        """
        pass

    def __ior__(self, *args, **kwargs): # real signature unknown
        """ Return self|=value. """
        pass

    def __isub__(self, *args, **kwargs): # real signature unknown
        """ Return self-=value. """
        pass

    def __iter__(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    def __ixor__(self, *args, **kwargs): # real signature unknown
        """ Return self^=value. """
        pass

    def __len__(self, *args, **kwargs): # real signature unknown
        """ Return len(self). """
        pass

    def __le__(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def __lt__(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __ne__(self, *args, **kwargs): # real signature unknown
        """ Return self!=value. """
        pass

    def __or__(self, *args, **kwargs): # real signature unknown
        """ Return self|value. """
        pass

    def __rand__(self, *args, **kwargs): # real signature unknown
        """ Return value&self. """
        pass

    def __reduce__(self, *args, **kwargs): # real signature unknown
        """ Return state information for pickling. """
        pass

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def __ror__(self, *args, **kwargs): # real signature unknown
        """ Return value|self. """
        pass

    def __rsub__(self, *args, **kwargs): # real signature unknown
        """ Return value-self. """
        pass

    def __rxor__(self, *args, **kwargs): # real signature unknown
        """ Return value^self. """
        pass

    def __sizeof__(self): # real signature unknown; restored from __doc__
        """ S.__sizeof__() -> size of S in memory, in bytes """
        pass

    def __sub__(self, *args, **kwargs): # real signature unknown
        """ Return self-value. """
        pass

    def __xor__(self, *args, **kwargs): # real signature unknown
        """ Return self^value. """
        pass

    __hash__ = None

　　下边就几个常用的方法进行练习，方便加深理解

测试数据如下

s1 = {1,2,3,4}
s2 = {2,4,6,7}

2.1 set的创建

set_1 = set() #创建一个空集合
set_2 = {123, "456"} #集合中包含元素123,"456"
#将list转换为set
list_1 = [1,2,3,4,4]
set_3 = set(list_1)
# set_3 = [1,2,3,4]

2.2 set.difference和set.difference_update 

s1 = {1,2,3,4}
s2 = {2,4,6,7}
s3 = a.difference(s2)
out: {1,3}
s1.difference_update(s2) 
print(s1)
out: {1,3}

2.3 set.symmetric_difference和set.symmetric_difference_update  交集的补集

 

s1 = {1,2,3,4}
s2 = {2,4,6,7}
s3 = s1.symmetric_difference(s2)
print(s3)
out: {1, 3, 6, 7}
s1.symmetric_difference_update(s2)
print(s1)
out: {1, 3, 6, 7}

2.4 set.intersection和set.intersection_update 交集

s1 = {1,2,3,4}
s2 = {2,4,6,7}           
s3 = s1.intersection(s2)
print(s3)
out: {2, 4}
s1.intersection_update(s2)
print(s1)
out: {2, 4}

2.5 union 全集

s1 = {1,2,3,4}
s2 = {2,4,6,7}    
s3 = s1.union(s2)
print(s3)
out: {1, 2, 3, 4, 6, 7}

 2.6 discard 与 add

　　discard 移除集合中某个元素，如果元素不存在，do nothing，同remove相比，remove如果元素不存在，会报keyError错误

       add      向集合中增加元素，如果元素存在，do nothing。

s1 = {1,2,3,4}
s1.discard(1)
s1.discard(5)
print(s1)

out: {2, 3, 4}

s1 = {1,2,3,4}
s1.add(2)
s1.add(5)
print(s1)

out: {1, 2, 3, 4, 5}

2.7 update

　　更新集合中的元素，已存在的更新，不存在的新增，更新对象可以是tuple 或者dict

    Update a set with the union of itself and others.

2.8 其他(非set必备特性)

li=[1,2,3] # 会执行list的 __init__方法
li()           # 会执行li的 __call__方法

list(tuple) 的原理：执行list.__init__ 构造函数，for循环tuple中的元素，然后添加到一个列表中

三、三元运算(或叫三目运算)

　　三元运算就是对简单的条件语句的缩写。

# 书写格式
 
result = 值1 if 条件 else 值2
 
# 如果条件成立，那么将 “值1” 赋值给result变量，否则，将“值2”赋值给result变量