Python进阶教程：常用标准库与实用技巧

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import os
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import sys
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# 当前工作目录
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print(os.getcwd())
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# 拼接路径（跨平台）
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path = os.path.join("data", "config.json")
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print(path)
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# 遍历目录
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for root, dirs, files in os.walk("."):
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    for f in files:
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        print(os.path.join(root, f))
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# 系统信息
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print(sys.version)          # Python 版本
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print(sys.platform)         # 操作系统
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print(sys.argv)             # 命令行参数

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from datetime import datetime, timedelta
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now = datetime.now()
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print(now)                     # 2026-08-14 10:30:00.123456
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print(now.strftime("%Y-%m-%d %H:%M:%S"))  # 格式化输出
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# 日期运算
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tomorrow = now + timedelta(days=1)
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print(tomorrow.strftime("%Y-%m-%d"))
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# 解析字符串为日期
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d = datetime.strptime("2026-08-14", "%Y-%m-%d")
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print(d.weekday())  # 星期几（0=周一）

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import json
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# Python 对象 -> JSON 字符串
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data = {"name": "Alice", "age": 20, "hobbies": ["reading", "coding"]}
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json_str = json.dumps(data, ensure_ascii=False, indent=2)
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print(json_str)
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# JSON 字符串 -> Python 对象
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parsed = json.loads(json_str)
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print(parsed["name"])  # Alice
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# 读写 JSON 文件
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with open("data.json", "w", encoding="utf-8") as f:
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    json.dump(data, f, ensure_ascii=False, indent=2)
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with open("data.json", "r", encoding="utf-8") as f:
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    loaded = json.load(f)

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import re
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text = "我的邮箱是 alice@example.com，备用邮箱 bob@test.org"
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# 查找所有邮箱
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emails = re.findall(r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}", text)
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print(emails)  # ['alice@example.com', 'bob@test.org']
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# 匹配并替换
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new_text = re.sub(r"\d+", "#", "订单号 12345 金额 99")
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print(new_text)  # 订单号 # 金额 #
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# 判断是否匹配
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if re.match(r"^\d{6}$", "123456"):
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    print("是6位数字")

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import random
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from collections import Counter, defaultdict
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# 随机数
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print(random.randint(1, 100))   # 1~100 随机整数
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print(random.choice(["a", "b", "c"]))  # 随机选择
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# 统计元素出现次数
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words = ["apple", "banana", "apple", "orange", "apple"]
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counter = Counter(words)
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print(counter.most_common(2))  # [("apple", 3), ("banana", 1)]
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# 带默认值的字典
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d = defaultdict(list)
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d["key"].append(1)  # 不会报 KeyError
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print(d)  # defaultdict(<class 'list'>, {'key': [1]})

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from itertools import chain, product, groupby
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from functools import lru_cache, partial
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# 链式拼接
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print(list(chain([1, 2], [3, 4])))  # [1, 2, 3, 4]
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# 笛卡尔积
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print(list(product([1, 2], ["a", "b"])))  # [(1,'a'), (1,'b'), (2,'a'), (2,'b')]
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# 缓存函数结果（性能优化）
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@lru_cache(maxsize=128)
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def fib(n):
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    if n < 2:
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        return n
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    return fib(n-1) + fib(n-2)
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print(fib(50))  # 瞬间返回 12586269025
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# 偏函数（固定部分参数）
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def power(base, exp):
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    return base ** exp
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square = partial(power, exp=2)
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print(square(5))  # 25

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import re
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import os
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from collections import Counter
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def word_frequency(filepath, top_n=10):
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    """统计文本文件中出现最多的前 N 个单词"""
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    if not os.path.exists(filepath):
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        print(f"文件不存在：{filepath}")
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        return
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    with open(filepath, "r", encoding="utf-8") as f:
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        text = f.read().lower()
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    # 用正则提取英文单词
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    words = re.findall(r"\b[a-z]+\b", text)
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    counter = Counter(words)
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    print(f"共 {len(words)} 个单词，前 {top_n} 个高频词：")
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    for word, count in counter.most_common(top_n):
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        print(f"{word}: {count} 次")
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# 使用示例
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word_frequency("article.txt", top_n=5)