split() - 分割字符串

text = "apple,banana,orange,grape"
fruits = text.split(",")
# 结果: ['apple', 'banana', 'orange', 'grape']

find()/index() - 定位子串

text = "Python is amazing"
position = text.find("amazing")
# 结果: 10

切片操作 - 提取子字符串

text = "2023-08-15_logfile.txt"
date = text[0:10]      # '2023-08-15'
ext = text[-3:]         # 'txt'

常用正则表达式模式

• \d 匹配数字
• \w 匹配字母数字
• . 匹配任意字符
• * 0次或多次重复
• + 1次或多次重复
• ? 0次或1次重复

实际应用示例

import re

# 提取电子邮件地址
text = "联系我: email@example.com 或 support@domain.org"
emails = re.findall(r'[\w\.-]+@[\w\.-]+', text)
# 结果: ['email@example.com', 'support@domain.org']

# 提取日期
log = "Error occurred on 2023-08-15 at 14:30:45"
date_match = re.search(r'\d{4}-\d{2}-\d{2}', log)
if date_match:
    date = date_match.group()  # '2023-08-15'

从日志文件提取错误信息

log_data = """
INFO: User login successful
ERROR: Database connection failed
WARNING: Disk space low
ERROR: File not found
"""

errors = re.findall(r'ERROR: (.+)', log_data)
# 结果: ['Database connection failed', 'File not found']

处理CSV数据提取特定列

csv_data = '''Name,Email,Phone
John Doe,john@example.com,555-1234
Jane Smith,jane@domain.org,555-5678
'''

# 提取所有电子邮件
emails = []
lines = csv_data.splitlines()[1:]  # 跳过标题行
for line in lines:
    emails.append(line.split(',')[1])
    
# 结果: ['john@example.com', 'jane@domain.org']

简单文本

使用内置字符串方法

模式匹配

正则表达式最强大

HTML/XML

BeautifulSoup最佳选择

自然语言

NLTK/spaCy最专业