【跟着AI学Python】Python进阶:字符串的高级用法

name = "Alice"age = 30print(f"Hello, {name}! You are {age} years old.")# → Hello, Alice! You are 30 years old.

price = 19.99tax = 0.08print(f"Total: ${price * (1 + tax):.2f}")# → Total: $21.59

x = 42y = "debug"print(f"{x=}, {y=}")  # 自动打印变量名和值！# → x=42, y='debug'

width = 10value = 3.14159print(f"Value: {value:{width}.2f}")# → Value:       3.14

from datetime import datetimeprint(f"当前时间: {datetime.now():%Y-%m-%d%H:%M}")# → 当前时间: 2026-03-19 20:45

name = "Bob"items = ["apple", "banana"]message = (    f"Dear {name},\n"    f"You ordered:\n"    f"{'\n'.join(f'- {item}'for item in items)}")print(message)

import relog_line = '192.168.1.1 - - [19/Mar/2026:20:40:00 +0000] "GET /index.html HTTP/1.1" 200'# 编译正则（提升性能）pattern = re.compile(r'(\d+\.\d+\.\d+\.\d+).*?\[(.*?)\]')match = pattern.search(log_line)if match:    ip, timestamp = match.groups()    print(f"IP: {ip}, 时间: {timestamp}")    # → IP: 192.168.1.1, 时间: 19/Mar/2026:20:40:00 +0000

email_pattern = re.compile(    r'''    \b              # 单词边界    [A-Za-z0-9._%+-]+  # 用户名    @               # @ 符号    [A-Za-z0-9.-]+    # 域名    \.              # 点    [A-Z|a-z]{2,}   # 顶级域    \b    ''', re.VERBOSE)

text = "  Hello, WORLD! 123  "# 清洗：去空格 → 小写 → 只保留字母和空格cleaned = (    text.strip()        .lower()        .translate(str.maketrans('', '', '0123456789'))  # 删除数字        .replace('!', ''))print(cleaned)  # → hello, world

# 创建删除表（删除标点）punctuation = "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~"translator = str.maketrans('', '', punctuation)text = "Hello, world! How are you?"print(text.translate(translator))  # → Hello world How are you

# str → bytes (编码)text = "你好"data = text.encode('utf-8')  # b'\xe4\xbd\xa0\xe5\xa5\xbd'# bytes → str (解码)restored = data.decode('utf-8')  # "你好"# 处理文件（始终指定 encoding！）withopen('file.txt', 'r', encoding='utf-8') as f:    content = f.read()  # str

# ❌ 危险！可能被注入user_input = "{error.__init__.__globals__}"template = "Hello, {}!".format(user_input)  # 潜在安全风险

from string import Templatetemplate = Template("Hello, $name!")safe_output = template.substitute(name=user_input)  # 不会执行代码！print(safe_output)  # Hello, {error.__init__.__globals__}!

import refrom collections import Counterdef analyze_logs(log_lines):    """分析日志，统计 IP 访问次数"""    ip_pattern = re.compile(r'^(\d+\.\d+\.\d+\.\d+) ')    ips = []    for line in log_lines:        match = ip_pattern.match(line)        if match:            ips.append(match.group(1))    return Counter(ips).most_common(5)# 使用logs = [    "192.168.1.1 ...",    "10.0.0.5 ...",    "192.168.1.1 ..."]top_ips = analyze_logs(logs)for ip, count in top_ips:    print(f"{ip}: {count} 次访问")