python正则表达式补充

 import re
 origin= "hello alex bcd alex 1ge alex acd 19"
 r=re.match("(?P<n1>h)(?P<n2>\w+)",origin)
 print(r.group())#获取匹配所有结果
 print(r.groups())#获取模型中匹配的分组结果
 print(r.groupdict())##获取模型中匹配的分组结果r=re.match("(？P<n1>h)(\w+)",origin)
 '''
 hello
 ('h', 'ello')
 {'n2': 'ello', 'n1': 'h'}
 '''

groups()就是显示选组（），而groupdict就是在分组加入一个关键字key

a = "alex"
n = re.findall('(\w)(\w)(\w)(\w)',a)
print(n)
n = re.findall('(\w){4}',a)
print(n)
n = re.findall("",a) #匹配空['', '', '', '', '']会比字符串多一个，就是最后再匹配一次
print(n)

str1 = "1abc2abcq3abc4abc"
t = re.findall('(\dabc)*',str1)#结是为什么是['2abc', '', '4abc', '']
#这个是因为匹配*为贪婪模式1abc2abc但括号取值取最后一个,到q是*可以为空,空匹配到，接着3abc4abc取后面4abc,完后还有一个空匹配
print(t)
运行结果

[('a', 'l', 'e', 'x')]
['x']
['', '', '', '', '']
['2abc', '', '4abc', '']

 import re
 def f(n):
     while True:
         if re.search('\d+\.?\d*[*/]\d+\.?\d*',n):#匹配小数点
            ret=re.search('\d+\.?\d*[*/]\d+\.?\d*',n).group()
            # print(ret)
            t=re.split('([*/])',ret)
            # print(t)
            if t[1] == '*':
                sum = float(t[0])*float(t[2])
            else:
                sum = float(t[0])/float(t[2])
            n1 = n.replace(ret,str(sum))
            # print(n1)
            n = n1
            t.clear()
         else:
            break
     while True:
         if re.search('\d+\.?\d*[+-]\d+\.?\d*',n):
            ret=re.search('\d+\.?\d*[+-]\d+\.?\d*',n).group()
            # print(ret)
            t=re.split('([+-])',ret)
            # print(t)
            if t[1] == '+':
                sum = float(t[0])+float(t[2])
            else:
                sum = float(t[0])-float(t[2])
            n1 = n.replace(ret,str(sum))
            # print(n1)
            n = n1
            t.clear()
         else:
            break
     return n
 n1 = '1+0*(3*4+(1+3))+23-2.51*0'
 print(n1)
 flag = True
 while flag:
     t1=re.split('\(([^()]+)\)',n1,1)#split分割出来去掉()
     if len(t1) == 3 :
         str1 = f(t1[1])#调用加减乘除函数
         t1[1]=str(str1)
         n1="".join(t1)
         # print(n1)
     else:
         flag = False
 n2=f(n1)
 print(n2)

 n='1+2*3+3*4'
 n1, count = re.subn('\*','/',n)
 print(n1,count)
运行结果
1+2/3+3/4 2