1、字符串基础 P62
字符串是不可变的
字符串是不可变的
>>> str='website'
>>> str[-2:]='yilia'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment
2、字符串格式化 ： % %s %.3f
>>> a = 'hello %s, %s'
>>> b = ('world', 'hello')
>>> a % b
'hello world, hello'
3、字符串方法
(1)find ：在一个较长的字符串中查找一个字符串，返回子字符串的首字母索引
>>> str = 'who are you ? i am a strudent'
>>> str.find("you")
8
>>> str.find("a", 2, -1) #提供起点和结束点
4
>>> str.find("a", 8, -1)
16
（2) join: 在队列中添加元素
>>> str = ['I', 'AM', 'YILIA']
>>> seq='+'
>>> str.join(seq)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'list' object has no attribute 'join'
>>> str = list(str)
>>> str.join(seq)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'list' object has no attribute 'join'
>>> str2 = ['a', 'b', 'c']
>>> str2.join(seq)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'list' object has no attribute 'join'
>>> str3 = 'a', 'b', 'c', 'dd'
>>> str3.join(seq)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'tuple' object has no attribute 'join'
>>> seq.join(str2)
'a+b+c'
>>> seq.join(str3)
'a+b+c+dd'
(3) lower: 返回字符串的小写字母
>>> 'I AM YILIA'.lower()
'i am yilia'
其它： upper、 islower、 isupper、 capitalize、 swapcase ...
(4) replace: 返回字符串的所有匹配想均被替换后的字符串, 原字符串不变
>>> str = 'i am amli'
>>> str.replace("am", 'yi')
'i yi yili'
>>> str
'i am amli'
(5) split: 将字符串分割成序列
>>> str
'i am amli'
>>> str.split('a')
['i ', 'm ', 'mli']
（6） strip: 去除字符串两侧的空格（不包含内部）， 返回新字符串，原字符串不变
>>> str = ' i am yilia '
>>> str.strip()
'i am yilia'
>>> str
' i am yilia '
（7） translate: 替换字符串中的单个字符，可同时替换多个