python如何用正则表达式提取字符串

import re
str = "a123b"
print(re.findall(r"a(.+?)b",str))
#输出['123']

import re
str = "a123b456b"
 
print(re.findall(r"a(.+?)b", str))
#输出['123']
#?控制只匹配0或1个,所以只会输出和最近的b之间的匹配情况
 
print(re.findall(r"a(.+)b", str))
#输出['123b456']
 
print(re.findall(r"a(.*)b", str))
#输出['123b456']

str = "a23b\na34b"
 
re.findall(r"a(\d+)b.+a(\d+)b", str)
#输出[]
#因为不能处理str中间有\n换行的情况
 
re.findall(r"a(\d+)b.+a(\d+)b", str, re.S)
#s输出[('23', '34')]

str = "a23b\na34b"
 
re.findall(r"^a(\d+)b", str)
#输出['23']
 
re.findall(r"^a(\d+)b", str, re.M)
#输出['23', '34']

import re
line ='192.168.0.1 25/Oct/2012:14:46:34 "GET /api HTTP/1.1" 200 44 "http://abc.com/search" 
"Mozilla/5.0"'
reg = re.compile('^(?P<remote_ip>[^ ]*) (?P<date>[^ ]*) "(?P<request>[^"]*)" 
(?P<status>[^ ]*) (?P<size>[^ ]*) "(?P<referrer>[^"]*)" "(?P<user_agent>[^"]*)"')
regMatch = reg.match(line)
linebits = regMatch.groupdict()
print(linebits)
for k, v in linebits.items() :
    print(k+": "+v)

import re
re.findall("\d+","asd1234")