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

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

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

3.  {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

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