>>> re.findall(r"a(d+?)","a23b") # 非贪婪模式
    ['2']
>>> re.findall(r"a(d+)","a23b")
    ['23']

>>> re.findall(r"a(d+)b","a23b")
    ['23']
>>> re.findall(r"a(d+?)b","a23b") #如果前后均有限定条件，则非匹配模式失效
    ['23']

>>> re.findall(r"a(d+)b.+a(d+)b","a23bna34b")
    []
>>> re.findall(r"a(d+)b.+a(d+)b","a23bna34b",re.S)
    [('23','34')]
>>>

>>> re.findall(r"^a(d+)b","a23bna34b")
    ['23']
>>> re.findall(r"^a(d+)b","a23bna34b",re.M)
    ['23','34']

>>> re.findall(r"a(d+)b","a23bna34b")
    ['23','43']

import re
n='''12 drummers drumming,
11 pipers piping, 10 lords a-leaping'''
p=re.compile('^d+')
p_multi=re.compile('^d+',re.MULTILINE) #设置 MULTILINE 标志
print re.findall(p,n) #['12']
print re.findall(p_multi,n) # ['12', '11']

import re
a = 'a23b'
print re.findall('a(d+?)',a) #['2']
print re.findall('a(d+)',a) #['23']
print re.findall(r'a(d+)b',a) #['23']
print re.findall(r'a(d+?)b',a) # ['23']

b='a23bna34b'
''' . 匹配非换行符的任意一个字符'''
print re.findall(r'a(d+)b.+a(d+)b',b) #[]
print re.findall(r'a(d+)b',b,re.M) # ['23', '34']
print re.findall(r'^a(d+)b',b,re.M) # ['23', '34']
print re.findall(r'a(d+)b',b) #['23','34'] 可以匹配多行
print re.findall(r'^a(d+)b',b) # ['23'] 默认^只会匹配符合正则的第一行
print re.findall(r'a(d+)b$',b) # ['34'] 默认$只会匹配符合正则的末行
print re.findall(r'a(d+)b',b,re.M) #['23', '34']
print re.findall(r'a(d+)b.?',b,re.M) # ['23', '34'] 表达式中的'.'匹配除换行符以外的字符，'?'匹配前一个字符0次或1次
print re.findall(r"a(d+)b", "a23bna34b") # ['23', '34']