#coding=utf-8import re# 正确的地址
ret = re.match("[\w]{4,20}@163\.com", "xiaoWang@163.com")
ret.group()# 不正确的地址
ret = re.match("[\w]{4,20}@163\.com", "xiaoWang@163.comheihei")
ret.group()# 通过$来确定末尾
ret = re.match("[\w]{4,20}@163\.com$", "xiaoWang@163.comheihei")
ret.group()

>>> re.match(r".*\bver\b", "ho ver abc").group()
'ho ver'>>> re.match(r".*\bver\b", "ho verabc").group()
Traceback (most recent call last):File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'>>> re.match(r".*\bver\b", "hover abc").group()
Traceback (most recent call last):File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'

>>> re.match(r".*\Bver\B", "hoverabc").group()
'hover'>>> re.match(r".*\Bver\B", "ho verabc").group()
Traceback (most recent call last):File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'>>> re.match(r".*\Bver\B", "hover abc").group()
Traceback (most recent call last):File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'>>> re.match(r".*\Bver\B", "ho ver abc").group()
Traceback (most recent call last):File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'

#coding=utf-8import reret = re.match("[1-9]?\d","8")
ret.group()ret = re.match("[1-9]?\d","78")
ret.group()# 不正确的情况
ret = re.match("[1-9]?\d","08")
ret.group()# 修正之后的
ret = re.match("[1-9]?\d$","08")
ret.group()# 添加|
ret = re.match("[1-9]?\d$|100","8")
ret.group()ret = re.match("[1-9]?\d$|100","78")
ret.group()ret = re.match("[1-9]?\d$|100","08")
ret.group()ret = re.match("[1-9]?\d$|100","100")
ret.group()

#coding=utf-8import reret = re.match("\w{4,20}@163\.com", "test@163.com")
ret.group()ret = re.match("\w{4,20}@(163|126|qq)\.com", "test@126.com")
ret.group()ret = re.match("\w{4,20}@(163|126|qq)\.com", "test@qq.com")
ret.group()ret = re.match("\w{4,20}@(163|126|qq)\.com", "test@gmail.com")
ret.group()