raw字符串（原始字符串)

所见即所得，例如

print('\n')

print(r'\n')

\n

len('\n')

1

len(r'\n')

2

Unicode 字符串

• ASCII码：每个字符都是以7位二进制数的方式存储在计算机内，ASCI字符只能表示95个可打印字符。
• Unicode：通过使用一个或多个字节来表示一个字符的方式突破了ASCII码的限制。

示例：

'\nabc'

'\nabc'

u'\nabc'

'\nabc'

u'刘备'

'刘备'

U'卓越'

'卓越'

Python转义字符

在需要在字符中使用特殊字符时，python用反斜杠(\)转义字符。如下表：

格式化操作

python字符串格式化符号:

格式化操作符辅助指令:

形式：
format%values

values的输入形式：

• 元组形式
• 字典形式（键作为format出现，字典作为values存在）

print('hello %s, %s enough!'%('world','happy'))

hello world, happy enough!

print('int：%d,str:%s,str:%s'%(1.0,['in list','i am list'],'i am str'))

int：1,str:['in list', 'i am list'],str:i am str

'%x'%100

'64'

'%X'%110

'6E'

'we are at %d%%'%100

'we are at 100%'

'%s is %d years old'%('Li',20)

'Li is 20 years old'

for i in range(1000,10000):
    a=int(i/1000)
    b=int(i/100)%10
    c=(int(i/10))%10
    d=i%10
    if a**4+b**4+c**4+d**4==i:
        print('%d=%d^4+%d^4+%d^4+%d^4'%(i,a,b,c,d))

1634=1^4+6^4+3^4+4^4
8208=8^4+2^4+0^4+8^4
9474=9^4+4^4+7^4+4^4

m.n 宽度与精度

'%.3f'%123.12345

'123.123'

'%.5s'%'hello world'

'hello'

'%+d'%4

'+4'

'%+d'%-4

'-4'

from math import pi
'%-10.2f'%pi

'3.14      '

'%10.4f'%pi

'    3.1416'

'My name is %(name)s,age is %(age)d,gender is %(gender)s'%{'name':'LiMing','age':28,'gender':'male'}

'My name is LiMing,age is 28,gender is male'

字符串模板

字符串对象Template对象存在与string模块中：

• 使用美元符号$定义代替换的参数
• 使用substitute()方法(缺少参数时会报错，KeyError异常) & safe_substitute()方法（缺少key时，直接显示参数字符串）进行参数替换

示例：

from string import Template
s=Template('There are ${how_many} nodes in the ${tree}')
print(s.substitute(how_many=32,tree='splay_tree'))

There are 32 nodes in the splay_tree

print(s.substitute(how_many=32))

---------------------------------------------------------------------------

KeyError                                  Traceback (most recent call last)

<ipython-input-4-6c5e84463638> in <module>()
----> 1 print(s.substitute(how_many=32))


D:\ProgramData\Anaconda3\lib\string.py in substitute(*args, **kws)
    124             raise ValueError('Unrecognized named group in pattern',
    125                              self.pattern)
--> 126         return self.pattern.sub(convert, self.template)
    127 
    128     def safe_substitute(*args, **kws):


D:\ProgramData\Anaconda3\lib\string.py in convert(mo)
    117             named = mo.group('named') or mo.group('braced')
    118             if named is not None:
--> 119                 return str(mapping[named])
    120             if mo.group('escaped') is not None:
    121                 return self.delimiter


KeyError: 'tree'

from string import Template
s=Template('There are ${how_many} nodes in the ${tree}')
print(s.safe_substitute(how_many=32))

There are 32 nodes in the ${tree}

Python 的字符串常用内建函数

1 S.capitalize() 返回一个首字母大写的字符串(str)：

a = "this is string example from runoob...wow!!!"
print ("a.capitalize() : ", a.capitalize())

a.capitalize() :  This is string example from runoob...wow!!!

2 S.lower -> Return a copy of the string S converted to lowercase

'HGKFKF'.lower()

'hgkfkf'

3 S.center(width[, fillchar])

参数：

• width:字符串的总宽度
• fillchar填充字符(默认为空格)

返回值：

• 一个指定的宽度width居中的字符串
• 如果width小于字符串宽度直接返回字符串，否则使用fillchar去填充

st = "[www.runoob.com]"
print ("st.center(40, '%') : ", st.center(40, '%'))

st.center(40, '%') :  %%%%%%%%%%%%[www.runoob.com]%%%%%%%%%%%%

4 S.count(sub[, start[, end]]) 该方法返回子字符串在字符串中出现的次数

• sub -- 搜索的子字符串
• start -- 字符串开始搜索的位置。默认为第一个字符。
• end -- 字符串中结束搜索的位置。默认为字符串的最后一个位置。

st="www.runoob.com"
sub='o'
print ("st.count('o') : ", st.count(sub))

sub='run'
print ("st.count('run', 0, 10) : ", st.count(sub,0,10))

st.count('o') :  3
st.count('run', 0, 10) :  1

5 bytes.decode(self, /, encoding='utf-8', errors='strict')

• encoding -- 要使用的编码，如"UTF-8"。
• errors -- 设置不同错误的处理方案。默认为'strict',意为编码错误引起一个UnicodeError。 其他可能得值有 'ignore', 'replace', 'xmlcharrefreplace', 'backslashreplace' 以及通过 codecs.register_error() 注册的任何值。

返回该方法返回解码后的字符串。

6 S.encode(encoding='utf-8', errors='strict') -> bytes

Python3 中str没有decode方法,但是可以使用bytes对象的decode()方法来解码给定的bytes对象，这个bytes对象可以由str.encode()来编码返回。

s = "中国"
s_utf8 = s.encode("UTF-8")
s_gbk = s.encode("GBK")

print(s)

print("UTF-8 编码：", s_utf8)
print("GBK 编码：", s_gbk)

print("UTF-8 解码：", s_utf8.decode('UTF-8','strict'))
print("GBK 解码：", s_gbk.decode('GBK','strict'))

中国
UTF-8 编码： b'\xe4\xb8\xad\xe5\x9b\xbd'
GBK 编码： b'\xd6\xd0\xb9\xfa'
UTF-8 解码： 中国
GBK 解码： 中国

7 S.find(sub[, start[, end]]) -> int

如果包含子字符串返回开始的索引值，否则返回-1。

str1 = "Runoob example....wow!!!"
str2 = "exam";
 
print (str1.find(str2))
print (str1.find(str2, 5))
print (str1.find(str2, 10))

7
7
-1

info = 'abca'
print(info.find('a'))      # 从下标0开始，查找在字符串里第一个出现的子串，返回结果：0

print(info.find('a', 1))   # 从下标1开始，查找在字符串里第一个出现的子串：返回结果3

print(info.find('3'))      # 查找不到返回-1

0
3
-1

8 S.join(iterable) -> str

Return a string which is the concatenation of the strings in the
iterable.

关于iterable参考python——聊聊iterable，sequence和iterators

s1 = "-"
s2 = ""
seq = ("r", "u", "n", "o", "o", "b") # 字符串序列
print (s1.join( seq ))
print (s2.join( seq ))

r-u-n-o-o-b
runoob

9 S.strip([chars]) -> str

• Return a copy of the string S with leading and trailing whitespace removed.
• If chars is given and not None, remove characters in chars instead.

st = "     this is string example....wow!!!     ";
print( st.lstrip() );
st = "88888888this is string example....wow!!!8888888";
print( st.lstrip('8') );
print( st.strip('8') );

this is string example....wow!!!     
this is string example....wow!!!8888888
this is string example....wow!!!

10 S.replace(old, new[, count]) -> str

• Return a copy of S with all occurrences of substring old replaced by new.
  
• If the optional argument count is given, only the first count occurrences are replaced.

st = "www.w3cschool.cc"
print ("菜鸟教程新地址：", st)
print ("菜鸟教程新地址：", st.replace("w3cschool.cc", "runoob.com"))

st = "this is string example....wow!!!"
print (st.replace("is", "was", 3))

菜鸟教程新地址： www.w3cschool.cc
菜鸟教程新地址： www.runoob.com
thwas was string example....wow!!!

11 S.split(sep=None, maxsplit=-1) -> list of strings

• Return a list of the words in S, using sep as the delimiter string.
  
• If maxsplit is given, at most maxsplit splits are done.
• If sep is not specified or is None, any whitespace string is a separator and empty strings are removed from the result.

st = "this is string example....wow!!!"
print (st.split( ))
print (st.split('i',1))
print (st.split('w'))

['this', 'is', 'string', 'example....wow!!!']
['th', 's is string example....wow!!!']
['this is string example....', 'o', '!!!']