python makestrans translate

    """
    1. makestrans()用法 

    语法: str.maketrans(intab, outtab]); 

    Python maketrans() 方法用于创建字符映射的转换表，对于接受两个参数的最简单的调用方式，
    第一个参数是字符串，表示需要转换的字符，第二个参数也是字符串表示转换的目标。
    注：两个字符串的长度必须相同，为一一对应的关系。 

    Python3.4已经没有string.maketrans()了，取而代之的是内建函数:
    bytearray.maketrans()、bytes.maketrans()、str.maketrans()
    """  

    intab = "abcd"
    outtab = "1234"
    str_trantab = str.maketrans(intab,outtab)  

    test_str = "csdn blog: http://blog.csdn.net/wirelessqa"  

    print (test_str.translate(str_trantab)) # 3s4n 2log: http://2log.3s4n.net/wirelessq1  

    """ 

    2. translate() 用法 

    根据参数table给出的表(包含 256 个字符)转换字符串的字符, 要过滤掉的字符放到 del 参数中。 

    语法:
    str.translate(table[, deletechars]);
    bytes.translate(table[, delete])
    bytearray.translate(table[, delete]) 

    若给出了delete参数，则将原来的bytes中的属于delete的字符删除，剩下的字符要按照table中给出的映射来进行映射
    """  

    # 若table参数为None，则只删除不映射
    print(b'http://www.csdn.net/wirelessqa'.translate(None, b'ts'))   #b'hp://www.cdn.ne/wireleqa'  

    # 若table参数不为NONE，则先删除再映射
    bytes_tabtrans = bytes.maketrans(b'abcdefghijklmnopqrstuvwxyz', b'ABCDEFGHIJKLMNOPQRSTUVWXYZ')
    print(b'http://www.csdn.net/wirelessqa'.translate(bytes_tabtrans, b'ts')) #b'HP://WWW.CDN.NE/WIRELEQA'  

    """
    3. 闭包: 它是个内层函数,由一个变量来指代,而这个变量对于外层包含它的函数来说是本地变量 

    """
    def make_adder(addend):
        def adder(augend):  #adder为内层函数
            return augend + addend
        return adder    

    a = make_adder(1)  #产生一个闭包,addend为1,注意return的是adder
    b = make_adder(2)  #产生另一个闭包,addend为2,注意return的是adder
    print (a(100), b(100))  #a(100)就相当于adder(100),adden之前为1,因此返回100+1  

    """
    4. 对translate方法的简单封装,使用起来更加方便
    frm : intab
    to : outtab
    delete : 指定删除字符
    keep: 指定保留字符
    delete和keep有重叠时，delete优先
    """
    def my_translator(frm = b'', to = b'', delete = b'', keep = None):    

        if len(to) == 1:
            to = to * len(frm) #如果to只有一个字符,将字符的数量跟frm相等,这样才能一一对应  

        #构建一个映射表
        trans = bytes.maketrans(frm, to)    

        if keep is not None: #如果有保留字
            allchars = bytes.maketrans(b'', b'')  # 获取空映射表的所有字符
            keep = keep.translate(allchars, delete)  # 从keep中去除delete中包含的字符，即keep与delete有重合时，优先考虑delete
            delete = allchars.translate(allchars, keep)  # delete为从全体字符中除去keep，即不在keep的都删掉    

        # 闭包
        def my_translate(s):
            return s.translate(trans, delete)    

        return my_translate    

    # 测试my_tranlator  

    # 只保留数字
    digits_only = my_translator(keep = b'0123456789')
    print(digits_only(b'http://www.csdn.net/wirelessqa 520520'))  #b'520520'  

    # 删除所有数字
    no_digits = my_translator(delete = b'0123456789')
    print(no_digits(b'http://www.csdn.net/wirelessqa 520520'))  #b'http://www.csdn.net/wirelessqa '  

    # 用*替换数字
    digits_to_hash = my_translator(frm = b'0123456789', to = b'*')
    print(digits_to_hash(b'http://www.csdn.net/wirelessqa 520520')) #b'http://www.csdn.net/wirelessqa ******'   

    # delete与keep有重合时的情况
    trans = my_translator(delete = b'20', keep = b'0123456789')
    print(trans(b'http://www.csdn.net/wirelessqa 520520'))  # b'55'