[a-z]+

import re
pattern = re.compile("[a-z]+")
result = pattern.search("hello world")
if result:
    print("匹配到的字符串为：", result.group())
else:
    print("没有匹配结果。")

匹配到的字符串为： hello

[a-zA-Z0-9]+

.

import re
pattern = re.compile("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}")
result = pattern.search("myemail@example.com")
if result:
    print("匹配到的字符串为：", result.group())
else:
    print("没有匹配结果。")

匹配到的字符串为： myemail@example.com

-?\d+

import re
text = "hello 123-456-7890 world"
pattern = re.compile(r"(\d{3}-\d{3}-\d{4})")
result = pattern.sub(r"\1987-654-321 hahaha", text)
print(result)

hello 123-456-7890 world

import re
text = "Python is a programming language"
pattern = re.compile(r"\s+")
result = pattern.sub('_', text)
print(result)

Python_is_a_programming_language

^\d{4}\-\d{1,2}\-\d{1,2}$

import re
pattern = re.compile(r"^\d{4}\-\d{1,2}\-\d{1,2}$")
result = pattern.search("2022-01-01")
if result:
    print("匹配到的日期为：", result.group())
else:
    print("没有匹配结果。")

匹配到的日期为： 2022-01-01

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$

import re
pattern = re.compile(r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$")
result = pattern.search("myemail@example.com")
if result:
    print("匹配到的邮箱地址为：", result.group())
else:
    print("没有匹配结果。")

匹配到的邮箱地址为： myemail@example.com

^(https?|ftp):\/\/[^\s\/.?#].[^\s]*

import re
pattern = re.compile(r"^(https?|ftp):\/\/[^\s\/.?#].[^\s]*")
result = pattern.search("https://www.example.com")
if result:
    print("匹配到的 URL 为：", result.group())
else:
    print("没有匹配结果。")

匹配到的 URL 为： https://www.example.com