\A:匹配字符串的开始
\b：匹配一个单词边界
取出a边界单词的个数
>>> len(re.findall(r"\ba"," ab abc add"))
3
\B:匹配非单词边界
\d:匹配任意一个数字范围【0-9】
- >>> re.match(r"\d+","123abc")
- <_sre.SRE_Match object at 0x000000000202A510>
\D:匹配任意一个非数字字符== [^\d]
- >>> re.match(r"\D+","ABC123").group()
- \'ABC\'
\s：匹配空白字符 练习
>>> print re.match(r"\s"," 13d")
<_sre.SRE_Match object at 0x0000000001F1A510>
\S:匹配非空白字符
>>> print re.match(r"\S","13d")
<_sre.SRE_Match object at 0x0000000001F1A510>
\w:匹配单个字符（数字或字母）
>>> print re.match(r"\w","13d")
<_sre.SRE_Match object at 0x0000000001F1A510>
\w+:匹配多个字符（数字或字母）
>>> print re.match(r"\w+","13d")
<_sre.SRE_Match object at 0x0000000001F1A510>
>>> re.match(r"\w+","13d")
<_sre.SRE_Match object at 0x0000000001F1A510>
>>> re.match(r"\w+","13d").group()
\'13d\'
>>> re.match(r"\D+","13d").group()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: \'NoneType\' object has no attribute \'group\'
\W:非单词字符，等价于[^\w]