文件 I/O

1. `open` 模式

模式	含义
`"r"`	只读（默认）
`"w"`	写入（清空原内容）
`"a"`	追加
`"x"`	排他创建（已存在则失败）
`"b"`	二进制（如 `"rb"`、`"wb"`）
`"t"`	文本（默认）

2. `with` 语句（推荐）

with 会在代码块结束时自动关闭文件，即使中间发生异常。

with 写入与读取

# 写入
with open("/tmp/hello.txt", "w", encoding="utf-8") as f:
    f.write("第一行\\n")
    f.write("第二行\\n")
 
# 读取
with open("/tmp/hello.txt", "r", encoding="utf-8") as f:
    print(f.read())

⚠️总是指定 encoding

跨平台文件读取务必带 encoding="utf-8"，否则 Windows 默认 GBK 会让中文乱码。

3. 多种读取方式

read / readline / readlines

with open("/tmp/poem.txt", "w", encoding="utf-8") as f:
    f.write("床前明月光\\n疑是地上霜\\n举头望明月\\n低头思故乡\\n")
 
with open("/tmp/poem.txt", encoding="utf-8") as f:
    print("--- read() ---")
    print(f.read())
 
with open("/tmp/poem.txt", encoding="utf-8") as f:
    print("--- readline() ---")
    print(f.readline(), end="")
    print(f.readline(), end="")
 
with open("/tmp/poem.txt", encoding="utf-8") as f:
    print("--- readlines() ---")
    print(f.readlines())

4. JSON 读写

JSON 序列化

import json
 
data = {
    "name": "Alice",
    "age": 30,
    "skills": ["Python", "Go", "Java"]
}
 
# 写入
with open("/tmp/user.json", "w", encoding="utf-8") as f:
    json.dump(data, f, ensure_ascii=False, indent=2)
 
# 读取
with open("/tmp/user.json", encoding="utf-8") as f:
    loaded = json.load(f)
    print(loaded)
    print(type(loaded["skills"]), loaded["skills"])

💡ensure_ascii=False

默认 json.dump 会把中文转成 \uXXXX。设 ensure_ascii=False 保留中文字符。

5. CSV 读写

CSV 读写

import csv
 
# 写入
rows = [
    ["name", "age", "city"],
    ["Alice", 30, "北京"],
    ["Bob", 25, "上海"],
]
with open("/tmp/people.csv", "w", encoding="utf-8", newline="") as f:
    writer = csv.writer(f)
    writer.writerows(rows)
 
# 读取
with open("/tmp/people.csv", encoding="utf-8", newline="") as f:
    for row in csv.DictReader(f):
        print(row)

6. 路径处理 `pathlib`

pathlib

from pathlib import Path
p = Path("/tmp") / "subdir" / "file.txt"
print(p)
print(p.name, p.suffix, p.parent)
 
# 创建目录
p.parent.mkdir(parents=True, exist_ok=True)
p.write_text("hello", encoding="utf-8")
print(p.exists(), p.read_text(encoding="utf-8"))

🎯 综合实战

学生成绩单

import json
from pathlib import Path
 
# 准备数据
students = [
    {"name": "Alice", "scores": [85, 92, 78]},
    {"name": "Bob",   "scores": [90, 88, 95]},
    {"name": "Carol", "scores": [76, 82, 80]},
]
 
# 写入 JSON
p = Path("/tmp/scores.json")
p.write_text(json.dumps(students, ensure_ascii=False, indent=2), encoding="utf-8")
 
# 读取并计算平均分
data = json.loads(p.read_text(encoding="utf-8"))
for s in data:
    avg = sum(s["scores"]) / len(s["scores"])
    print(f"{s['name']}: 平均 {avg:.1f}")

小结

✅ open(path, mode, encoding="utf-8") 打开文件
✅ with 自动关闭
✅ read() / readline() / readlines() 多种读法
✅ json.dump/load 处理 JSON
✅ csv.writer / DictReader 处理 CSV
✅ pathlib.Path 面向对象地处理路径

🎉 Python 8 章完结！你已掌握 Python 的核心语法与常用库。接下来进入 Go 语言的学习。