From 03eddc109af7fa4c5b1ba841342bdcdf06fa1240 Mon Sep 17 00:00:00 2001
From: lkjing2021345 <1908499668@qq.com>
Date: Sat, 22 Aug 2026 01:09:38 +0800
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+# Day_13 · 文件读写与 JSON：让数据活到下次运行
+
+> 预计耗时：25~30 分钟
+> 程序一关，变量就没了。想让数据存下来（这就是"持久化"，数据库干的事），先从文件开始。
+> Django 的数据库、缓存的本质，都是"把数据存起来再读回来"。
+
+## 今日知识点
+
+- 写文件：`with open("note.txt", "w") as f: f.write(内容)`（`w` = 覆盖写）
+- 读文件：`with open("note.txt", "r") as f: 内容 = f.read()`
+- `with` 会自动关文件，不用手动 close
+- **JSON**：一种"把字典/列表变成文本"的格式，`json.dumps` 变文本、`json.loads` 变回数据
+- 为什么重要：HTTP 接口传输的数据、配置文件，全是 JSON 格式
+
+## 先学（教程）
+
+- 菜鸟教程（"文件方法"一节，看 open/read/write 即可）：https://www.runoob.com/python3/python3-file-methods.html
+- 菜鸟教程（"JSON"一节）：https://www.runoob.com/python3/python3-json.html
+- B站黑马教程（看讲"文件操作"的几集）：https://www.bilibili.com/video/BV1qW4y1a7fU/
+
+## 任务（后做）
+
+新建 `day13.py`：
+
+1. 写入再读回：
+   ```python
+   text = input("写一句话存起来：")
+   with open("note.txt", "w", encoding="utf-8") as f:
+       f.write(text)
+
+   with open("note.txt", "r", encoding="utf-8") as f:
+       content = f.read()
+   print("读回来的是：", content)
+   ```
+   运行后确认同目录出现了 `note.txt`，且内容一致。（注意 `encoding="utf-8"`，否则中文会乱码。）
+2. 用 JSON 存字典：
+   ```python
+   import json
+
+   user = {"name": "张三", "age": 18, "city": "青岛"}
+
+   with open("user.json", "w", encoding="utf-8") as f:
+       json.dump(user, f, ensure_ascii=False)   # ensure_ascii=False 让中文可读
+
+   with open("user.json", "r", encoding="utf-8") as f:
+       loaded = json.load(f)
+
+   print(loaded["name"], loaded["age"])         # 从文件里还原的字典
+   ```
+3. **进阶（加分）**：把 Day_5 的"三个用户列表"用 `json.dump` 存进 `users.json`，
+   再读回来遍历打印每个人的名字。
+
+## 完成标准
+
+- [ ] note.txt 和 user.json 出现在同目录，读回内容一致
+- [ ] 能说出 `json.dump` 和 `json.load` 各是干嘛的
+- [ ] （进阶）用户列表存取成功
+
+**提交方式**：把 `day13.py` 代码贴在当日工单评论里。
+
+## 参考解答（先做再看）
+
+```python
+text = input("写一句话存起来：")
+with open("note.txt", "w", encoding="utf-8") as f:
+    f.write(text)
+with open("note.txt", "r", encoding="utf-8") as f:
+    print("读回来的是：", f.read())
+
+import json
+user = {"name": "张三", "age": 18, "city": "青岛"}
+with open("user.json", "w", encoding="utf-8") as f:
+    json.dump(user, f, ensure_ascii=False)
+with open("user.json", "r", encoding="utf-8") as f:
+    loaded = json.load(f)
+print(loaded["name"], loaded["age"])
+
+# 进阶
+users = [
+    {"name": "张三", "age": 19},
+    {"name": "李四", "age": 20},
+    {"name": "王五", "age": 18},
+]
+with open("users.json", "w", encoding="utf-8") as f:
+    json.dump(users, f, ensure_ascii=False)
+with open("users.json", "r", encoding="utf-8") as f:
+    for u in json.load(f):
+        print(u["name"])
+```