老齐python-基础2(字符串)

1、字符串

    1.1索引和切片

        索引:

>>> lang = "study python"
>>> lang[0]
's'
>>> lang[1]
't'
>>> "study python"[0]
's'

        字符串中对应的索引:

         通过字符串找索引:

>>> lang.index("p")
6

         字符串切片:

>>> lang = "study python"
>>> lang[2:9]
'udy pyt'

>>> lang = 'study python'
>>> b = lang[1:]              #得到从1号到末尾的字符，这时最后那个序号不用写
>>> b
'tudy python'
>>> c = lang[:]                #得到所有的字符
>>> c
'study python'                 
>>> d = lang[:10]            #得到从第一个到10号之前的字符
>>> d
'study pyth'

>>> e = lang[0:10]
>>> e
'study pyth'
>>> lang[1:11]   #如果冒号后面有数字，所得到的切片不包含数字所对应的序号(前包括,后不包括)
'tudy pytho'
>>> lang[1:]
'tudy python'

>>> lang[1:12]
'tudy python'
>>> lang[1:13]
'tudy python'

   1.2字符串基本操作

       len():求序列长度   #返回值为一个整数

       +:连接2个序列

       *:重复序列元素

       in:判断元素是否存在于序列中

       max():返回最大值

       min():返回最小值  

    +:

>>> str1 = 'python'
>>> str2 = 'lisp'
>>> str1 + str2       #字符串连接
'pythonlisp'
>>> str1 + "&" + str2
'python&lisp'

    in:

>>> str1 = "python"
>>> str2 = "lisp"
>>> "p" in str1        #判断某个字符传是不是在另外一个字符串内，包含返回True 返回False
True
>>> "th" in str1
True
>>> "l" in str2
True
>>> "l" in str1
False

    max、min、ord、chr:

>>> max(str1)   #最值比较，按照ASCLL码
'y'
>>> min(str1)
'h'

>>> ord("y")    #查看ASCLL码对应的顺序
121
>>> ord("h")
104
>>> chr(104)    #通过ASCLL码顺对应顺序查找字符
'h'

 字符串比较

>>> 'a' > 'b'
False
>>> 'a' < 'b'
True
>>> "abc" > "aaa"   #按照顺序比较字符串 1如果相等对比2，直到对比出大小
True
>>> "abc" < "a c"
Fals

重复字符

>>> a * 3
'hellohellohello'
>>> print("-" * 30)
------------------------------

     1.3字符串格式化输出

        老用法不提倡:

>>> "I like %s" % "python"
'I like python'
>>> "I like %s" % "Pascal"
'I like Pascal'

        新用法提倡:

>>> "I like {0} and {1}".format("python","cangloshi")
'I like python and cangloshi'

>>> "I like {0:10} and {1:>15}".format("python","canglaoshi")
'I like python     and      canglaoshi'
#{0:10} 为python预留10个字符，{1:>15}右对齐预留15字符

>>> "I like {0:^10} and {1:^15}".format("python","canglaoshi")
'I like   python   and   canglaoshi   '
#居中显示

>>> "I like {0:.2} and {1:^10.4}".format("python","canglaoshi")
'I like py and    cang   '
#显示第一个元素的前连个字符，第二个元素占10个字符 居中显示前4个元素

>>> "She is {0:d} years old and the breast is {1:f}cm".format(28,90.143598)
'She is 28 years old and the breast is 90.143598cm'
#数字操作

>>> "She is {0:4d} years old and the breast is {1:6.2f}cm".format(28,90.143598)
'She is   28 years old and the breast is  90.14cm'
#变量1占用4字节默认右对齐，变量2占用6字节右对齐，保留小数2位

>>> "She is {0:04d} years old and the breast is {1:06.2f}cm".format(28,90.143598)
'She is 0028 years old and the breast is 090.14cm'
#位数不足用0补

>>> "I like {lang} and {name}".format(lang="python",name='canglaoshi')
'I like python and canglaoshi'

>>> data = {"name":"Canglaoshi","age":28}
>>> "{name} is {age}".format(**data)
'Canglaoshi is 28'
#字典用法

    1.4常用字符串方法

dir(str)
#获取字符串所有方法
help(str.isalpha)
#多去方法帮助

        1)判断是否全是字母

        2)根据分隔符分割字符串

        3)去掉字符串两头的空格

        4)字符大小写转换

            S.upper()     #S中的字母转换为大写
            S.lower()     #S中的字母转换为小写
            S.capitalize()   #将首字母转换为大写
            S.isupper()   #判断S中的字母是否全是大写
            S.islower()   #判断S中的字母是否全是小写
            S.istitle()   #判断S是否是标题模式，即字符串中所有的单词拼写首字母为大写，且其它字母为小写

        5)用join拼接字符串

        6)替换字符串 

             te = te.replace('test','OK')

>>> "python".isalpha() #判断是否全是字母
True
>>> "python2".isalpha()
False

>>> a = "I LOVE PYTHON"  #按照空格分割,生成列表
>>> a.split(" ")
['I', 'LOVE', 'PYTHON']
>>> b = "www.itdiffer.com"
>>> b.split(".")
['www', 'itdiffer', 'com']

>>> b = " hello "  
>>> b.strip()   #去掉两边的空格
'hello'
>>> b     #未改变字符串本身
' hello '
>>> b.lstrip()  #去掉左边空格
'hello '
>>> b.rstrip()  #去掉右边空格
' hello

>>> a = "TAJZHANG"  
>>> a.istitle()     #判断大写，返回布尔值
False
>>> a = "tAJZHANG"
>>> a.istitle()
False
>>> a = "Taj,Zhang"
>>> a.istitle()
True

>>> a = "This is a Book"
>>> a.istitle()
False
>>> b = a.title()
>>> b
'This Is A Book'
>>> b.istitle()
True
>>> a = "Tajzhang"
>>> a.isupper()
False
>>> a.upper().isupper()  #全大写判断
True
>>> a.islower()
False
>>> a.lower().islower()  #全小写判断
True

>>> b = 'www.itdiffer.com'
>>> c = b.split(".")
>>> c
['www', 'itdiffer', 'com']
>>> ".".join(c)
'www.itdiffer.com'
>>> "*".join(c)
'www*itdiffer*com'

    1.5字符编码

      计算机中的编码:ASCLL、Unicode、UTF-8、gbk、gbk2312

      python3中默认就是utf8不需要声明，python2中开头声明'# -*- coding: utf-8 -*-' 显示中文才不会报错

>>> import sys
>>> sys.getdefaultencoding()  #查看目前的编码
'utf-8'
>>> ord("Q")   #ASCLL码互转
81
>>> chr(81) 
'Q'

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