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'
#一個"."就是匹配除 \n (換行符)以外的任意一個字符
print(re.findall(r'a.b',str))#['aab', 'aab']
#*前面的字符出現0次或以上
print(re.findall(r'a*b',str))#['aab', 'b', 'ab', 'aab', 'b']
#貪婪，匹配從.*前面為開始到后面為結束的所有內容
print(re.findall(r'a.*b',str))#['aabbabaabb']
#非貪婪，遇到開始和結束就進行截取，因此截取多次符合的結果，中間沒有字符也會被截取
print(re.findall(r'a.*?b',str))#['aab', 'ab', 'aab']
#非貪婪，與上面一樣，只是與上面的相比多了一個括號，只保留括號的內容
print(re.findall(r'a(.*?)b',str))#['a', '', 'a']
 
str = '''aabbab
         aabbaa
         bb'''#后面多加了2個b
#沒有把最后一個換行的aab算進來
print(re.findall(r'a.*?b',str))#['aab', 'ab', 'aab']
#re.S不會對\n進行中斷
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']