Python re.findall中正则表达式(.*?)和参数re.S使用

def findall(pattern, string, flags=0):
    """Return a list of all non-overlapping matches in the string.
    If one or more capturing groups are present in the pattern, return
    a list of groups; this will be a list of tuples if the pattern
    has more than one group.
    Empty matches are included in the result."""
    return _compile(pattern, flags).findall(string)

import re
 
str = 'aabbabaabbaa'
#一个"."就是匹配除 \n (换行符)以外的任意一个字符
print(re.findall(r'a.b',str))#['aab', 'aab']
#*前面的字符出现0次或以上
print(re.findall(r'a*b',str))#['aab', 'b', 'ab', 'aab', 'b']
#贪婪，匹配从.*前面为开始到后面为结束的所有内容
print(re.findall(r'a.*b',str))#['aabbabaabb']
#非贪婪，遇到开始和结束就进行截取，因此截取多次符合的结果，中间没有字符也会被截取
print(re.findall(r'a.*?b',str))#['aab', 'ab', 'aab']
#非贪婪，与上面一样，只是与上面的相比多了一个括号，只保留括号的内容
print(re.findall(r'a(.*?)b',str))#['a', '', 'a']
 
str = '''aabbab
         aabbaa
         bb'''#后面多加了2个b
#没有把最后一个换行的aab算进来
print(re.findall(r'a.*?b',str))#['aab', 'ab', 'aab']
#re.S不会对\n进行中断
print(re.findall(r'a.*?b',str,re.S))#['aab', 'ab', 'aab', 'aa\n         b']

str = 'aabbabaabbaa'

print(re.findall(r'a.b',str))
['aab', 'aab']

print(re.findall(r'a*b',str))
['aab', 'b', 'ab', 'aab', 'b']

print(re.findall(r'a.*b',str))
['aabbabaabb']

print(re.findall(r'a.*?b',str))
['aab', 'ab', 'aab']

print(re.findall(r'a(.*?)b',str))
['a', '', 'a']

str = '''aabbab
         aabbaa
         bb'''

print(re.findall(r'a.*?b',str))
['aab', 'ab', 'aab']

print(re.findall(r'a.*?b',str,re.S))
['aab', 'ab', 'aab', 'aa\n         b']