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Python字符串
（1）在python中，可以用单引号（’ ’）或者双引号(“ ”)来表示字符串,效果都是一样的，可以用‘/’来进行特殊字符的转义。
>>> ‘spam eggs‘ # single quotes
‘spam eggs‘
>>> ‘doesn\‘t‘ # use \‘ to escape the single quote...
"doesn‘t"
>>> "doesn‘t" # ...or use double quotes instead
"doesn‘t"
>>> ‘"Yes," he said.‘
‘"Yes," he said.‘
>>> "\"Yes,\" he said."
‘"Yes," he said.‘
>>> ‘"Isn\‘t," she said.‘
‘"Isn\‘t," she said.‘
（2）如果你不想字符前面加上 \ 将被解释为特殊字符，可以通过在第一个引号前面加上r来表示的原始字符串。
>>> print(‘C:\some\name‘) # here \n means newline!
C:\some
ame
>>> print(r‘C:\some\name‘) # note the r before the quote
C:\some\name
（3）字符串可以跨多个行。一种方法使用三重引号:"""......"""或 ‘ ‘...‘ ‘。
>>>print("""
Usage: thingy[OPTIONS]
-h Display this usagemessage
-H hostname Hostname to connect to
""")
Usage: thingy[OPTIONS]
-h Display this usagemessage
-H hostname Hostname to connect to
(4)可以通过在字符串的行尾加上“/”来使两行变成一行。
>>>print("""
Usage: thingy[OPTIONS]\
-h Display this usagemessage
-H hostname Hostname to connect to
""")
Usage: thingy[OPTIONS] -h Display this usagemessage
-H hostname Hostname to connect to
（5）可以连接字符串（粘结在一起）+ 运算符，复制使用 *:
>>>print(3 * ‘un‘ + ‘ium‘)
Unununium
（6）两个或多个字符串（即封闭引号之间的字符串）紧邻的将自动连接。
>>> ‘Py‘ ‘thon‘
‘Python‘
但是，这仅仅适用于字符串文本之间，不适用于变量以及表达式。
>>> prefix = ‘Py‘
>>> prefix ‘thon‘ # can‘t concatenate a variable and a string literal
...
SyntaxError: invalid syntax
>>> (‘un‘ * 3) ‘ium‘
...
SyntaxError: invalid syntax
如果想要连接变量和字符串文本，需要使用+
>>> prefix + ‘thon‘
‘Python‘
当你想要打破长字符串时，此功能是特别有用的︰
>>> text = (‘Put several strings within parentheses ‘
... ‘to have them joined together.‘)
>>> text
‘Put several strings within parentheses to have them joined together.‘
（7）字符串可以索引 （下标），第一个字符的下标为0。Python中没有单独的字符类型;字符是大小为 1 的字符串︰
>>> word = ‘Python‘
>>> word[0] # character in position 0
‘P‘
>>> word[5] # character in position 5
‘n‘
索引也可以是负数，从右边开始计数，从-1开始︰
>>> word[-1] # last character
‘n‘
>>> word[-2] # second-last character
‘o‘
>>> word[-6]
‘P‘
注意：当索引超出字符串大小时，会报错。
>>> word[42] # the word only has 6 characters
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: string index out of range
（8）除了索引，还支持切片。索引用来获取单个字符，切片允许您获取子字符串︰
>>> word[0:2] # characters from position 0 (included) to 2 (excluded)
‘Py‘
>>> word[2:5] # characters from position 2 (included) to 5 (excluded)
‘tho‘
可以看出，切片中，开始的位置被包括，而结束的位置不包含。这样，
s[:i]+s[i:]永远等于s:
>>> word[:2] + word[2:]
‘Python‘
>>> word[:4] + word[4:]
‘Python‘
切片指数具有有用的默认值;省略的第一个索引默认为零，省略第二个索引默认为被切成字符串的大小。
>>> word[:2] # 从0到2的字符
‘Py‘
>>> word[4:] # 从4到结尾的字符
‘on‘
>>> word[-2:] #从-2到结尾的字符
‘on‘
不同于索引超出会报错，切片不一定会报错：
>>> word[4:42]
‘on‘
>>> word[42:]
‘‘
但是，负数索引超出的时候，切片会报错：
>>> print(word[-10,3])
Traceback (most recent call last):
File "<pyshell#39>", line 1, in <module>
print(word[-10,3])
TypeError: string indices must be integers
（9）python中字符串是不可变的，所以不能使用索引或者切片对字符串进行改变。
>>> word[0] = ‘J‘
...
TypeError: ‘str‘ object does not support item assignment
>>> word[2:] = ‘py‘
...
TypeError: ‘str‘ object does not support item assignment
如果你需要一个新字符串，你需要重新建一个字符串
>>> ‘J‘ + word[1:]
‘Jython‘
>>> word[:2] + ‘py‘
‘Pypy‘
(10)内建函数len()返回字符串的长度
>>> s = ‘supercalifragilisticexpialidocious‘
>>> len(s)
34
当然,字符串还有很多其他的性质和方法,以后会继续讲解。
Python字符串