import re
pattern = '^a...s$'
test_string = 'abyss'
result = re.match(pattern, test_string)

if result:
   print("Search successful.")
else:
   print("Search unsuccessful.")

import re 
string = 'hello 12 hi 89. Howdy 34'
pattern = '\d+'
print("Entered String=",string)
result = re.findall(pattern, string)
print("The numbers in the above string",result)

Entered String= hello 12 hi 89. Howdy 34
The numbers in the above string ['12', '89', '34']

match = re.search(pattern, str)

import re
string = "Python is fun"
#检查'Python'是否在开头
match = re.search('\APython', string)
if match:
   print("pattern found inside the string")
else:
   print("pattern not found")

pattern found inside the string

#程序以删除所有空格为例
import re
#多行字符串
string = 'abc 12\
de 23 \n f45 6'
print("Orginal String =",string)
#匹配所有空白字符
pattern = '\s+'
#空字符串
replace = ''
new_string = re.subn(pattern, replace, string)
print("New String=",new_string)

Orginal String = abc 12de 23 
 f45 6
New String= ('abc12de23f456', 4)

import re
string = 'Twelve:12 Eighty nine:89.'
pattern = '\d+'
result = re.split(pattern, string)
print(result)

['Twelve:', ' Eighty nine:', '.']

import re

string = 'Twelve:12 Eighty nine:89 Nine:9.'
pattern = '\d+'

//maxsplit = 1
//仅在第一次出现时进行拆分
result = re.split(pattern, string, 1)
print(result)

['Twelve:', ' Eighty nine:89 Nine:9.']

re.sub(pattern, replace, string)

#程序以删除所有空格为例
import re
#多行字符串
string = 'abc 12\ de 23 \n f45 6'
#匹配所有空白字符
pattern = '\s+'
#空字符串
replace = ''
new_string = re.sub(pattern, replace, string)
print(new_string)

abc12\de23f456

import re
#多行字符串
string = "abc 12\
de 23 \n f45 6"
#匹配所有空白字符
pattern = '\s+'
replace = ''
new_string = re.sub(r'\s+', replace, string, 1)
print(new_string)

abc12de 23 
 f45 6

import re
string = '39801 356, 2102 1111'
#三位数字后跟空格后跟两位数字
pattern = '(\d{3}) (\d{2})'
#match变量包含一个Match对象。
match = re.search(pattern, string)
if match:
   print(match.group())
else:
   print("pattern not found")

801 35

>>> match.group(1)
'801'

>>> match.group(2)
'35'

>>> match.group(1, 2)
('801', '35')

>>> match.groups()
('801', '35')

match.start()，match.end()和match.span()

# start()函数返回匹配的子字符串的开始索引。同样，end()返回匹配的子字符串的结束索引。

>>> match.start()
2

>>> match.end()
8

# span()函数返回一个元组，其中包含匹配部分的开始和结束索引。

>>> match.span()
(2, 8)

# match.re和match.string

# 匹配对象的re属性返回正则表达式对象。同样，string属性返回传递的字符串。

>>> match.re
re.compile('(\d{3}) (\d{2})')

>>> match.string
'39801 356, 2102 1111'

import re
string = '\n and \r are escape sequences.'
result = re.findall(r'[\n\r]', string)
print(result)

['\n', '\r']