python正则表达式re.match()匹配多个字符方法的实现

1.  *表示匹配任意多个字符   \\d*表示匹配任意多个数字字符

import re
 
text = "123h1ello world"
text1 = "123Hello world456"
text2 = "hello world"
 
res = re.match("\\d*", text)  
res1 = re.match("\\d*", text1)
res2 = re.match("\\d*", text2)
 
print(res.group())
print(res1.group())
print(res2.group())

输出结果为

123
123

Process finished with exit code 0

示例2：*

需求：匹配出，一个字符串第一个字母为大小字符，后面都是小写字母并且这些小写字母可有可无

import re
#注意是前一个字符
ret = re.match("[A-Z][a-z]*","M")
print(ret.group())

ret = re.match("[A-Z][a-z]*","AaBcDE")
print(ret.group())

ret = re.match("[A-Z][a-z]*","Aabcdef")
print(ret.group())

#运行结果
M
Aa
Aabcdef

2.  +表示匹配1个或者多个任意字符   \\w+表示匹配一个或多个字母，数字或下划线

import re
 
text = "he+llo world"
text1 = "Hello world456"
text2 = "+hello world"
 
res = re.match("\\w+", text)
res1 = re.match("\\w+", text1)
res2 = re.match("\\w+", text2)
 
print(res.group())
print(res1.group())
print(res2)

输出结果为

he
Hello
None

Process finished with exit code 0

示例2：+

需求：匹配出，变量名是否有效

import re
names = ["name1","_name","2_name","__name__"]
for i in names:
  ret = re.match("[a-zA-Z_]+[\\w]*",i)
  if ret:
    print("变量名 %s 符合要求" % ret.group())
  else:
    print("变量名 %s 非法" % i)

#运行结果
变量名 name1 符合要求
变量名 _name 符合要求
变量名 2_name 非法
变量名 __name__ 符合要求

3.  ?表示匹配0个或一个字符     \\w?表示匹配0或1个字母，数字或下划线

import re
 
text = "he+llo world"
text1 = "Hello world456"
text2 = "+hello world"
 
res = re.match("\\w?", text)
res1 = re.match("\\w?", text1)
res2 = re.match("\\w?", text2)
 
print(res.group())
print(res1.group())
print(res2.group())

输出结果为

h
H

Process finished with exit code 0

示例2：？

需求：匹配出0到99之间的数字

import re

ret = re.match("[1-9]?[0-9]","7")
print(ret.group())

ret = re.match("[1-9]?\\d","33")
print(ret.group())

ret = re.match("[1-9]?\\d","09")
print(ret.group())

#运行结果
7
33
0 # 这个结果并不是想要的，利用$才能解决

4.  {m}表示匹配m个字符    \\d{11}表示匹配11个数字字符

import re
 
text = "he+llo world"
text1 = "Hello world456"
text2 = "hello world"
 
res = re.match("\\w{2}", text)
res1 = re.match("\\w{3}", text1)
res2 = re.match("\\w{4}", text2)
 
print(res.group())
print(res1.group())
print(res2.group())

输出结果为

he
Hel
hell

Process finished with exit code 0

示例2：{m}
需求：匹配出，8到20位的密码，可以是大小写英文字母、数字、下划线

import re
ret = re.match("[a-zA-Z0-9_]{6}","123a3g45678")
print(ret.group())

ret = re.match("[[a-zA-Z0-9_]{8,20}","1ad3123456addfcasdef")
print(ret.group())

#运行结果
123a3g
1ad3123456addfcasdef

5.   {m,n}表示匹配m-n个字符   \\w{2,4}表示匹配2-4个字符

import re
 
text = "hello world"
text1 = "Helloworld456"
text2 = "hello world"
 
res = re.match("\\w{2,5}", text)
res1 = re.match("\\w{6,8}", text1)
res2 = re.match("\\w{20,25}", text2)
 
print(res.group())
print(res1.group())
print(res2)

hello
Hellowor
None

Process finished with exit code 0