Python open函数 - 文件打开读写操作

# open()函数基本语法
open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)

# r模式 - 只读（默认）
with open("example.txt", "r") as f:
    content = f.read()
    print(content)

# w模式 - 写入（覆盖）
with open("output.txt", "w") as f:
    f.write("Hello, World!\n")
    f.write("这是第二行\n")

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

# rb模式 - 读取二进制文件
with open("image.png", "rb") as f:
    data = f.read()
    print(f"文件大小: {len(data)} 字节")

# wb模式 - 写入二进制文件
with open("copy.png", "wb") as f:
    f.write(data)

# r+模式 - 读写模式
with open("data.txt", "r+") as f:
    content = f.read()
    f.write("\n新添加的内容")

# 推荐：始终指定UTF-8编码
with open("chinese.txt", "w", encoding="utf-8") as f:
    f.write("中文内容\n")
    f.write("Hello World\n")

with open("chinese.txt", "r", encoding="utf-8") as f:
    content = f.read()
    print(content)

# 输出结果
# 中文内容
# Hello World

# errors参数处理编码错误
# 'ignore' - 忽略无法解码的字符
with open("mixed_encoding.txt", "r", encoding="utf-8", errors="ignore") as f:
    content = f.read()

# 'replace' - 用?替换无法解码的字符
with open("mixed_encoding.txt", "r", encoding="utf-8", errors="replace") as f:
    content = f.read()

# 'strict' - 遇到错误抛出异常（默认行为）
with open("mixed_encoding.txt", "r", encoding="utf-8", errors="strict") as f:
    content = f.read()

# 推荐做法：使用with语句
with open("data.txt", "r", encoding="utf-8") as f:
    content = f.read()
# 文件自动关闭，无需手动f.close()

# 不推荐：需要手动关闭
f = open("data.txt", "r", encoding="utf-8")
try:
    content = f.read()
finally:
    f.close()  # 必须手动关闭

# 同时打开多个文件
with open("input.txt", "r", encoding="utf-8") as infile, \
     open("output.txt", "w", encoding="utf-8") as outfile:
    
    for line in infile:
        processed = line.upper()
        outfile.write(processed)

print("文件处理完成！")

# 高效读取大文件（内存友好）
line_count = 0
with open("large_file.txt", "r", encoding="utf-8") as f:
    for line in f:
        line_count += 1
        # 处理每一行
        if "error" in line.lower():
            print(f"第{line_count}行发现错误: {line.strip()}")

print(f"总行数: {line_count}")

# read() - 读取整个文件为字符串
with open("example.txt", "r", encoding="utf-8") as f:
    full_content = f.read()
    print(type(full_content))  # <class 'str'>

# readlines() - 读取所有行返回列表
with open("example.txt", "r", encoding="utf-8") as f:
    lines = f.readlines()
    print(type(lines))  # <class 'list'>
    print(f"共{len(lines)}行")
    for i, line in enumerate(lines, 1):
        print(f"第{i}行: {line.strip()}")

# 写入多行数据
data = ["第一行数据", "第二行数据", "第三行数据"]

with open("data_output.txt", "w", encoding="utf-8") as f:
    for item in data:
        f.write(item + "\n")

# 使用writelines()更高效
with open("data_output.txt", "w", encoding="utf-8") as f:
    f.writelines(line + "\n" for line in data)

print("数据写入完成！")