Python正则表达式字符串扩展

使用Python的正则表达式可以方便地进行字符串匹配和处理。正则表达式是一种强大的文本模式匹配工具，通过使用一些特殊字符和语法规则，可以快速地找到符合特定模式的字符串。本文将介绍Python正则表达式的一些常用扩展，以及一些实际应用案例。

python
import re
text = "Hello, World!\nHello, Python!\nHello, Universe!"
pattern = r"^Hello.*World$"
matches = re.findall(pattern, text, re.MULTILINE)
print(matches)

['Hello, World!']

python
import re
text = "Hello, world! hello, Python! HELLO, universe!"
pattern = r"^hello.*"
matches = re.findall(pattern, text, re.IGNORECASE)
print(matches)

['Hello, world!', 'hello, Python!', 'HELLO, universe!']

python
import re
text = "Today is 2019-01-01."
pattern = r"(?P\d{4})-(?P\d{2})-(?P\d{2})"
matches = re.search(pattern, text)
year = matches.group("year")
month = matches.group("month")
day = matches.group("day")
print(year, month, day)

2019 01 01

python
import re
with open("email.txt", "r") as file:
    text = file.read()
pattern = r"\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b"
matches = re.findall(pattern, text)
for match in matches:
    print(match)