字符串详解
没那么多废话，直接介绍字符串使用。继续往下看~~~
字符串定义：
*1.引号包围，不可变（指的是不可以对字符串进行修改）得序列（凡是能够通过索引取值的都是序列）。
*2.不可变对象（字符串）在调用自身方法时，不会改变原有内容。
字符串创建：
' '
" "
""" 或者 '''
1.单引号和双引号，字符串可以嵌套使用，不可以交叉使用。
2.三引号经常用于多行注释
>>> print '''hello,jim my name is bob!
... how are you?
... welcome to china!
... byebye
... '''
hello,jim my name is bob!
how are you?
welcome to china!
byebye
3.字符串中的\转义字符
>>> 'let\'s go jim we are go to school!'
"let's go jim we are go to school!"
字符串中的\n
>>> print '''hello,zhaoming\nhow are you?'''
hello,zhaoming
how are you?
4.字符串之 原始字符串 r
>>> print r'C:\now\abc\bcd\efg\aaa\nnn\bmb'
C:\now\abc\bcd\efg\aaa\nnn\bmb
>>> 'C:\now'
'C:\now'
>>> print 'C:\now'
C:
ow
>>> print 'C:\\now'
C:\now
5.字符串拼接 (通过加号+拼接)
>>> name = "zhangshan"
>>> age = '25'
>>> name + age
'zhangshan25'
>>> name = "zhangshan"
>>> age = 25
>>> name + str(age)
'zhangshan25'
>>> name + str(age) + 'how are you?'
'zhangshan25how are you?'
6.字符串格式化输出
1.通过% 格式化操作 %s替换所有类型 %d替换整型 %f替换浮点型
>>> name = 'lishi'
>>> age = 155
>>> 'hello,%s my age is %s'%(name,age)
'hello,lishi my age is 155'
>>> 'hello,%s my age is %s'%(age,name)
'hello,155 my age is lishi'
>>> 'hello,%d my age is %s'%(name,age)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: %d format: a number is required, not str
>>> 'hello,%s my age is %d'%(name,age)
'hello,lishi my age is 155'
7.判断变量类型内置函数
type(a)
isinstance(a,b) a为变量，b为类型 检查是否匹配 匹配为真 不匹配为假
>>> isinstance(111,int)
True
>>> isinstance('',int)
False
>>> isinstance('',str)
True
>>> isinstance(11.00,float)
True
8.字符串复制 *
>>> 'hello' + 'zhanshan' + 'nihao---->'*3
'hellozhanshannihao---->nihao---->nihao---->'
9.字符串判断
>>> 'zhang' in 'zhangshan'
True
>>> '12' in 'zhangshan'
False
>>> 'zhang' not in 'zhangshan'
False
10.字符串索引
索引从0开始，默认取值方向从左到右
单个取值
>>> 'hello_world'
'hello_world'
>>> 'hello_world'[0]
'h'
>>> 'hello_world'[1]
'e'
>>> 'hello_world'[2]
'l'
普通截取 [开始端：结束端] 包含开始端 不包含结尾端
>>> 'hello_world'
>>> demo[0:11]
'hello_world'
>>> demo[:]
'hello_world'
>>> demo[0:4]
'hell'
>>> demo[0:3]
'hel'
步长截取 [开始端：结束端：步长值] 包含开始端 不包含结尾端 步长按照步长值减1隔取
>>> demo = 'hello_world'
>>> demo[::2]
'hlowrd'
>>> demo[::]
'hello_world'
>>> demo[::2]
'hlowrd'
>>> demo[:5:2]
'hlo'
>>> demo[:5:2]
>>> demo[::3]
'hlwl'
反向截取 [开始端：结束端] 包含开始端 不包含结尾端
>>> demo = 'hello_world'
>>> demo[-1]
'd'
>>> demo[-2]
'l'
>>> demo[-3]
'r'
>>> demo[-5:-1]
'worl'
>>> demo[-5:0]
''
>>> demo[-5:]
'world'
特殊情况
>>> demo = 'hello_world'
>>> demo[5:0]
''
>>> demo[5:0]
''
>>> demo[0:12]
'hello_world'
>>> demo[0:13]
'hello_world'
>>> demo = 'hello_world'
>>> demo[-1:-5]
''
>>> demo[-3:-5]
''
>>> demo[-20:]
'hello_world'
11.字符串常用操作函数
dir(str) 查看字符串的用法
>>> demo.find('m')
-1
>>> demo = 'hello_werld'
>>> demo.find('e')
1
>>> demo.find('w')
6
2.字符串-split()函数（分隔函数）
>>> demo = 'hello_werld'
>>> demo.split('e')
['h', 'llo_w', 'rld']
>>> demo = 'hello_world'
>>> demo.split('e')
['h', 'llo_world']
>>> demo.split('_')
['hello', 'world']
>>> demo.split('')
3.字符串-upper()函数 将字符串中所有的字符变成大写
(不可变对象调用自身方法不会改变自身的原有内容)
>>> demo = 'hello_world'
>>> demo.upper()
'HELLO_WORLD'
>>> demo
'hello_world'
>>> abc=demo.upper()
>>> abc
'HELLO_WORLD'
>>> demo
'hello_world'
>>>
4.字符串-lower()函数 将字符串中所有的字符变成大写
>>> abc='HELLO_WORLD'
>>> abc
'HELLO_WORLD'
>>> abc.lower()
'hello_world'
>>>
5.字符串的替换-replace（a,b） a是要替换的原内容 b是替换的新内容
>>> url='www.baidu.com'
>>> url
'www.baidu.com'
>>> url.replace('baidu','sina')
'www.sina.com'
>>> url
'www.baidu.com'
>>> demo=url.replace('baidu','sina')
>>> demo
'www.sina.com'
6.字符串的- join函数（分隔）
>>> url='www.baidu.com'
>>> ':'.join(url)
'w:w:w:.:b:a:i:d:u:.:c:o:m'
>>> username='zhangshan,lishi,wangwu'
>>> ':'.join(username)
'z:h:a:n:g:s:h:a:n:,:l:i:s:h:i:,:w:a:n:g:w:u'
>>> username='zhangshan,lishi,wangwu'
>>> username.split(',')[0]
'zhangshan'
>>> username.split(',')[1]
'lishi'
>>> username.split(',')[2]
'wangwu'
7.字符串的strip 忽略字符串前后空格
>>> username=' zhangshan,lishi,wangwu '
>>> username
' zhangshan,lishi,wangwu '
>>> username.strip()
'zhangshan,lishi,wangwu'
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