Python中as关键字的作用实例解析

try:
    10 / 0  # 触发 ZeroDivisionError 异常，Python 会创建该异常的对象
except ZeroDivisionError as e:  # 将异常对象绑定到变量 e
    print(f"错误描述：{e}")  # 访问异常对象的信息，输出：division by zero
    print(f"异常类型：{type(e)}")  # 输出：<class 'ZeroDivisionError'>

try:
    data = {"name": "张三"}
    print(data["age"])  # 可能触发 KeyError
    # 10 / 0  # 可能触发 ZeroDivisionError
except (KeyError, ZeroDivisionError) as e:
    # 通过 type(e) 区分异常类型，针对性处理
    if isinstance(e, KeyError):
        print(f"键不存在：{e}")
    else:
        print(f"除数为0：{e}")

# 大数据/数据分析领域的常见别名
import numpy as np  # numpy → np
import pandas as pd  # pandas → pd
import matplotlib.pyplot as plt  # matplotlib.pyplot → plt
# 爬虫领域的常见别名
import requests as req  # requests → req
from bs4 import BeautifulSoup as bs  # BeautifulSoup → bs

from module1 import func as func1
from module2 import func as func2
# 调用时不会冲突
func1()
func2()

from datetime import datetime as dt  # datetime 类 → dt
from os import path as osp  # os.path → osp
print(dt.now())  # 等价于 datetime.now()
print(osp.exists("test.txt"))  # 等价于 os.path.exists()

# 将文件对象绑定到变量 f，通过 f 操作文件
with open("data.csv", "r", encoding="utf-8") as f:
    content = f.read()  # 读取文件内容
    lines = f.readlines()  # 按行读取

# with 块结束后，文件会自动关闭，无需手动 f.close()

import sqlite3
# 将数据库连接对象绑定到变量 conn
with sqlite3.connect("test.db") as conn:
    cursor = conn.cursor()
    cursor.execute("SELECT * FROM users")  # 执行SQL
    result = cursor.fetchall()

import requests
# 将响应对象绑定到变量 res
with requests.get("https://www.baidu.com") as res:
    print(res.status_code)  # 获取响应状态码
    print(res.text)  # 获取响应内容

import re
pattern = r"(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})"
match = re.match(pattern, "2025-12-22")
# 访问命名分组，等价于 match.group(1)、match.group(2)
print(match.group("year"))  # 输出：2025
print(match.group("month"))  # 输出：12

from typing import TypeAlias
# 定义别名：MovieData 是字典类型的别名
MovieData: TypeAlias = dict[str, str | int]
# 使用别名
def process_movie(data: MovieData) -> None:
    print(data["name"])
process_movie({"name": "肖申克的救赎", "score": 9.7})

import aiohttp
import asyncio
async def fetch_url(url: str):
    # 异步上下文管理器，绑定响应对象到 res
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as res:
            return await res.text()
# 执行异步函数
asyncio.run(fetch_url("https://www.baidu.com"))

try:
    10 / 0
except ZeroDivisionError as e:
    print(e)  # 有效
print(e)  # 报错：NameError: name 'e' is not defined