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What are the Python sequence types?

Jul 20, 2017 pm 03:31 PM
pythonsequencetype

Python sequence type

序列:字符、列表、元组

    所有序列都支持迭代
    序列表示索引为非负整数的有序对象集合
    字符和元组属于不可变序列,列表可变

1)Character

    字符串字面量:把文本放入单引号、双引号或三引号中;
    '    ''    '''
        >>> str1 = ' hello, fanison '
        >>> type(str1)
        str
    
    如果要使用unicode编码,则在字符之前使用字符u进行标识
        >>> str2 = u'你好,fanison'
        >>> type(str2)
        unicode
        
    文档字串:模块、类或函数的第一条语句是一个字符的话,该 字符串就成为文档字符串,可以使用__doc__属性引用;
        例:
            >>> def printName():
                    "the function is print hello"
                    print 'hello'
            >>> printName.__doc__
            
    运算符:
        索引运算符          s[i]        返回一个序列的元素i
        切片运算符          s[i:j]      返回一个切片
        扩展切片运算符      s[i:j:stride]
      
        例:
            >>> str3 = 'hello,fanison'
            >>> str2[0:]
            'hello,fanison'      返回所有元素
            >>> str2[0:7]
            'hello,f'            返回索引7之前的所有元素
            >>> str2[0:7:2]
            'hlof'               返回从索引0到6内步径为2的元素,即隔一个取一个
            >>> str2[7:0:-2]        
            'a,le'               从索引7处倒着隔一个取一个取到索引1处
            >>> str2[-4:-1]
            'iso'                从索引-4处取到-2处       
            >>> str2[-4::-1]
            'inaf,olleh'         从-4处到开始处倒着取
        注意:
            步径为正表示  正着取,索引从小到大          i  j
        
    支持运算:
        索引、切片、min()、max()、len()等
        
            len(s)              s中的元素个数
            min(s)              s的最小值
            max(s)              s的最大值
            
   支持方法:
        S.index(sub [,start [,end]])            找到指定字符串sub首次出现的位置
        S.upper()                               将一个字符串转换为大写形式
        S.lower()                               将一个字符串转化为小写形式
        S.join(t)                               使用s作为分隔符连接序列t中的字符串
                    >>> l1 = list(str1)
                    >>> l1
                    ['h', 'e', 'l', 'l', 'o', ',', 'f', 'a', 'n', 'i', 's', 'o', 'n']
                    >>> ''.join(l1)
                    'hello,fanison'             使用空字符作为分隔符连接列表l1
       S.replace(old, new[, count])             替换一个字符串
                    >>> str1.replace('fan','FAN')
                    'hello,FANison'
    注意:
        使用 help()获取其帮助
                >>> help(str.join)

2)List

列表:容器类型
         任意对象的有序集合,通过索引访问其中的元素,可变对象,长度可变,异构,任意嵌套
     
      支持在原处修改
            修改指定的索引元素,修改指定的分片,删除语句,内置方法
            
         >>> list1 = [ 1,2,3,'x','n' ]
         >>> list1[1]=56
         >>> print list1
         [1, 56, 3, 'x', 'n']
         >>> list1[1:3]=[]              会删除索引1到索引3之前的元素
         >>> print list1
         [1, 'x', 'n']   
         >>> del(list1[1])              使用del函数删除list索引为1的元素
         >>> print list1
         [1, 'n']
            注意:
                 因为支持原处修改,不会改变内存位置,可使用  id() 查看其位置变化
       
       内置方法:
                 L.count(value)                     计算value值出现的次数
                 L.append(object)                   将一个新元素追加到L末端                    
                 L.extend(iterable)                 增加合并列表(第二个列表内容会以单个元素追加至末端)
                        >>> l1 = [ 1,2,3 ]
                        >>> l2 = [ 'x','y','z']
                        >>> l1.append(l2)
                        >>> l1
                        [1, 2, 3, ['x', 'y', 'z']]          使用append方法会以其原有存在形式追加
                        >>> l1 = [ 1,2,3 ]
                        >>> l1.extend(l2)
                        >>> l1
                        [1, 2, 3, 'x', 'y', 'z']            注意两种增加的区别
                L.pop([index])                      返回元素index并从列表中移除它,如果省略则返回并移除列表最后一个元素
                L.remove(key)                       移除值为key的元素
                        >>> l1 = [ 'x',2,'abc',16,75 ]
                        >>> l1.pop(2)                       pop方法是按索引移除
                        'abc'
                        >>> l1
                        ['x', 2, 16, 75]
                        >>> l1.remove(16)                   remove方法是按值移除
                        >>> l1
                        ['x', 2, 75]  
                L.index(value)                        指定值首次出现的位置
                L.insert(index, object)               在索引index处插入值
                        >>> l1.insert(1,'abc')
                        >>> l1
                        ['x', 'abc', 2, 75]
                L.sort()                              排序
                L.reverse()                           逆序
                        >>> l1.sort()
                        [2, 75, 'abc', 'x']
                        >>> l1.reverse()
                        ['x', 'abc', 75, 2]
                        
        l1 + l2: 合并两个列表,返回一个新的列表;不会修改原列表;
                        >>> l1 = [ 1,2,3]
                        >>> l2 = [ 'x','y','z']
                        >>> l1 + l2
                        [1, 2, 3, 'x', 'y', 'z']
                        
        l1 * N: 把l1重复N次,返回一个新列表; 
                        >>> l1 * 3
                        [1, 2, 3, 1, 2, 3, 1, 2, 3]         使用id()查看是否生成新列表
        
        成员关系判断字符:  
                        in              用法:   item in container
                        not in               item not in container
                            >>> l1 = [ 'x','y',3 ]
                            >>> 'y' in l1
                            True
                            >>> 'x' not in l1
                            False
                            
       列表解析:[]
       
       列表复制方式:
            浅复制:两者指向同一内存对象
                    >>> l1 = [ 1,2,3,4 ]
                    >>> l2 = l1
                    >>> id(l1) == id(l1)
                    True                            可以看出两者内存地址相同
                    >>> l1.append('x')
                    >>> print l1
                    [ 1,2,3,4,'x' ]
                    >>> print l2
                     [ 1,2,3,4,'x' ]
            深复制:两者指向不同内存对象
                    1)导入copy模块,使用deepcoop方法
                     >>> import copy
                     >>> l3 = copy.deepcopy(l1)
                     >>> id(l3) == id(l1)
                     False                          地址不同
                     
                    2)复制列表的所有元素,生成一个新列表
                    >>> l4 = l1[:]              
                    >>> print l4
                    [ 1,2,3,4,'x' ]
                    >>> l1.append(6)
                    >>> print l1
                    [ 1,2,3,4,'x',6 ]               l1改变
                    >>> print l4
                    [ 1,2,3,4,'x' ]                 l4不变

3)Tuple

    表达式符号:()

    容器类型
        任意对象的有序集合,通过索引访问其中的元素,不可变对象,长度固定,异构,嵌套
    
    常见操作:
        ()                      
                    >>> t1 = ( 1,2,3,'xyz','abc')
                    >>> type(t1)
                    tuple
                    >>> len(t1)
                    5
                    >>> t2 = ()                             定义一个空元组
                    >>> t3 = ( , )
                    SyntaxError: invalid syntax             报错:使用逗号分隔的条件是最少要有一个元素
        
        (1,)
                    >>> t1[:]
                    ( 1,2,3,'xyz','abc' )
                    >>> t1[1:]
                    (2, 3, 'xyz', 'abc')
    
        (1,2)       
                    >>> t1[1:4]
                    (2, 3, 'xyz')
                    >>> t4 = 'x',1,'yz',45,[2,4,6]              注意!!!这样也可以生成元组
                    >>> t4  
                    ('x', 1, 'yz', 45, [2, 4, 6])

        t1 + t4: 合并两个元组,返回一个新的元组;不会修改原元组;
                    >>> t1 + t4
                    (1, 2, 3, 'xyz', 'abc', 'x', 1, 'yz', 45, [2, 4, 6])
        
       
       t1 * N:  把l1重复N次,返回一个新元组; 
                    >>> t1 * 3
                    (1, 2, 3, 'xyz', 'abc', 1, 2, 3, 'xyz', 'abc', 1, 2, 3, 'xyz', 'abc')

        成员关系判断
                in
                not in
     
        注意:
            虽然元组本身不可变,但如果元组内嵌套了可变类型的元素,那么此类元素的修改不会返回新元组;
                例:
                    >>> t4 = ('x', 1, 'yz', 45, [2, 4, 6])
                    >>> id(t4)
                    44058448
                    >>> t4[4]                           
                    [2, 4, 6]
                    >>> t4[4].pop()                     弹出列表内一个元素
                    6
                    >>> print t4[4]
                    [2, 4]
                    >>> print t4
                    ('x', 1, 'yz', 45, [2, 4]) 
                    >>> id(t4)
                    44058448                            由此可见,对元组内列表内的修改也会使元组发生改变,没有返回新元组

4)Sequence operation summary

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