IO编程 (Input/Output)

# 读取整个文件内容
with open("test.txt", "r", encoding="utf-8") as f:
    content = f.read()
    print(content)

# 读取固定字节数
with open("test.txt", "r") as f:
    chunk = f.read(100)   # 读取前100个字符

# 逐行读取
with open("test.txt", "r") as f:
    for line in f:
        print(line.rstrip())   # rstrip() 去除换行符

# 读取所有行到列表
with open("test.txt", "r") as f:
    lines = f.readlines()

# 读取到列表（更简洁）
with open("test.txt", "r") as f:
    lines = list(f)

# readline() 逐行读取
with open("test.txt", "r") as f:
    line1 = f.readline()
    line2 = f.readline() 

# 写入文件（覆盖）
with open("output.txt", "w", encoding="utf-8") as f:
    f.write("Hello, World!\n")
    f.write("第二行")

# 追加模式
with open("output.txt", "a") as f:
    f.write("\n追加的内容")

# 写入多行
lines = ["第一行\n", "第二行\n", "第三行\n"]
with open("output.txt", "w") as f:
    f.writelines(lines)

# 使用 join 写入多行（推荐）
lines = ["第一行", "第二行", "第三行"]
with open("output.txt", "w") as f:
    f.write("\n".join(lines))

# 写入字节串
with open("binary.bin", "wb") as f:
    f.write(b"Hello Bytes") 

from io import StringIO, BytesIO

# StringIO - 操作字符串
buffer = StringIO()
buffer.write("Hello ")
buffer.write("World!")
print(buffer.getvalue())   # Hello World!

# 从字符串创建 StringIO
source = StringIO("初始内容\n第二行")
print(source.readline())

# BytesIO - 操作字节
byte_buffer = BytesIO()
byte_buffer.write(b"Hello")
byte_buffer.write(b" Bytes")
print(byte_buffer.getvalue())   # b'Hello Bytes'

# 实际应用：格式化输出
from io import StringIO

def format_output(items):
    buffer = StringIO()
    for i, item in enumerate(items, 1):
        buffer.write(f"{i}. {item}\n")
    return buffer.getvalue()

print(format_output(["苹果", "香蕉", "橙子"])) 

import json

# Python 对象 → JSON 字符串
data = {
    "name": "张三",
    "age": 25,
    "scores": [90, 85, 92],
    "is_student": True,
    "address": None
}

json_str = json.dumps(data, ensure_ascii=False, indent=2)
print(json_str)

# JSON 字符串 → Python 对象
parsed = json.loads(json_str)
print(parsed["name"])

# 写入 JSON 文件
with open("data.json", "w", encoding="utf-8") as f:
    json.dump(data, f, ensure_ascii=False, indent=2)

# 读取 JSON 文件
with open("data.json", "r", encoding="utf-8") as f:
    loaded_data = json.load(f)

print(loaded_data) 

import json
from datetime import datetime

# 自定义日期编码器
class DateEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        return super().default(obj)

# 使用
data = {
    "event": "发布会",
    "time": datetime.now()
}

json_str = json.dumps(data, cls=DateEncoder, ensure_ascii=False)
print(json_str) 

import pickle

# 序列化对象
data = {"name": "张三", "scores": [90, 85, 92]}
serialized = pickle.dumps(data)
print(type(serialized))   # <class 'bytes'>

# 反序列化
deserialized = pickle.loads(serialized)
print(deserialized)

# 写入文件
with open("data.pkl", "wb") as f:
    pickle.dump(data, f)

# 读取文件
with open("data.pkl", "rb") as f:
    loaded = pickle.load(f) 

import csv

# 写入 CSV
with open("users.csv", "w", newline="", encoding="utf-8") as f:
    writer = csv.writer(f)
    writer.writerow(["姓名", "年龄", "城市"])
    writer.writerow(["张三", 25, "北京"])
    writer.writerow(["李四", 30, "上海"])

# 读取 CSV
with open("users.csv", "r", encoding="utf-8") as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)

# 使用字典方式读写
with open("users.csv", "r", encoding="utf-8") as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(f"姓名: {row['姓名']}, 年龄: {row['年龄']}")

# 写入字典 CSV
with open("users_dict.csv", "w", newline="", encoding="utf-8") as f:
    fieldnames = ["姓名", "年龄", "城市"]
    writer = csv.DictWriter(f, fieldnames=fieldnames)
    writer.writeheader()
    writer.writerow({"姓名": "王五", "年龄": 28, "城市": "广州"})