Python文件操作

文件对象 = open(文件名, 模式)

# 以只读方式打开文件
file = open('example.txt', 'r')

# 以写入方式打开文件（如果文件不存在会创建）
file = open('data.txt', 'w')

# 以追加方式打开文件
file = open('log.txt', 'a')

# 以二进制方式读取图片
file = open('image.jpg', 'rb')

# 方法1：使用read()读取全部内容
file = open('example.txt', 'r', encoding='utf-8')
content = file.read()
print(content)
file.close()

# 方法2：使用with语句，自动关闭文件
with open('example.txt', 'r', encoding='utf-8') as file:
    content = file.read()
    print(content)
# 文件会自动关闭，不需要调用close()

# 读取单行
with open('example.txt', 'r', encoding='utf-8') as file:
    first_line = file.readline()
    print("第一行:", first_line)

# 读取所有行到列表
with open('example.txt', 'r', encoding='utf-8') as file:
    lines = file.readlines()
    for line in lines:
        print(line.strip())  # strip()移除首尾空白字符

# 直接遍历文件对象（推荐用于大文件）
with open('example.txt', 'r', encoding='utf-8') as file:
    for line_num, line in enumerate(file, 1):
        print(f"第{line_num}行: {line.strip()}")

# 写入模式（会覆盖原有内容）
with open('output.txt', 'w', encoding='utf-8') as file:
    file.write("这是第一行文本\n")
    file.write("这是第二行文本\n")
    number = 42
    file.write(f"这是一个数字：{number}\n")

# 追加模式（在文件末尾添加）
with open('output.txt', 'a', encoding='utf-8') as file:
    file.write("这是在末尾添加的内容\n")

# 使用writelines方法
lines = [
    "第一行内容\n",
    "第二行内容\n", 
    "第三行内容\n"
]

with open('multi_line.txt', 'w', encoding='utf-8') as file:
    file.writelines(lines)

# 使用循环写入
data = ["苹果", "香蕉", "橙子", "葡萄"]
with open('fruits.txt', 'w', encoding='utf-8') as file:
    for fruit in data:
        file.write(fruit + '\n')

with open('example.txt', 'r+', encoding='utf-8') as file:
    # 获取当前位置
    position = file.tell()
    print(f"当前位置：{position}")
    
    # 读取前10个字符
    content = file.read(10)
    print(f"前10个字符：{content}")
    
    # 移动到文件开头
    file.seek(0)
    print("移动后位置：", file.tell())
    
    # 移动到第5个字符
    file.seek(5)
    print("从第5个字符开始：", file.read())

# 在文件特定位置插入内容
def insert_content(filename, position, new_content):
    with open(filename, 'r+', encoding='utf-8') as file:
        content = file.read()
        file.seek(0)
        file.write(content[:position] + new_content + content[position:])

# 使用示例
insert_content('test.txt', 5, '插入的内容')

# 复制图片文件
def copy_image(source, destination):
    with open(source, 'rb') as src_file:
        with open(destination, 'wb') as dst_file:
            content = src_file.read()
            dst_file.write(content)
    print(f"图片已从 {source} 复制到 {destination}")

# 使用示例
copy_image('photo.jpg', 'photo_backup.jpg')

def save_student_scores(students, filename='scores.txt'):
    """保存学生成绩到文件"""
    with open(filename, 'w', encoding='utf-8') as file:
        file.write("姓名,语文,数学,英语\n")
        for name, scores in students.items():
            line = f"{name},{scores['chinese']},{scores['math']},{scores['english']}\n"
            file.write(line)
    print("学生成绩已保存")

def load_student_scores(filename='scores.txt'):
    """从文件加载学生成绩"""
    students = {}
    try:
        with open(filename, 'r', encoding='utf-8') as file:
            lines = file.readlines()
            # 跳过标题行
            for line in lines[1:]:
                name, chinese, math, english = line.strip().split(',')
                students[name] = {
                    'chinese': int(chinese),
                    'math': int(math),
                    'english': int(english)
                }
    except FileNotFoundError:
        print("成绩文件不存在")
    return students

# 使用示例
students_data = {
    '张三': {'chinese': 85, 'math': 92, 'english': 78},
    '李四': {'chinese': 90, 'math': 88, 'english': 95},
    '王五': {'chinese': 76, 'math': 85, 'english': 80}
}

save_student_scores(students_data)
loaded_data = load_student_scores()

# 显示成绩
print("\n学生成绩：")
for name, scores in loaded_data.items():
    avg_score = (scores['chinese'] + scores['math'] + scores['english']) / 3
    print(f"{name}: 语文{scores['chinese']} 数学{scores['math']} 英语{scores['english']} 平均{avg_score:.1f}")

def write_log(message, level="INFO", filename="app.log"):
    """写入日志文件"""
    from datetime import datetime
    
    timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
    log_entry = f"[{timestamp}] {level}: {message}\n"
    
    with open(filename, 'a', encoding='utf-8') as file:
        file.write(log_entry)
    
    print(f"日志已记录：{log_entry.strip()}")

def read_recent_logs(filename="app.log", lines=10):
    """读取最近的日志"""
    try:
        with open(filename, 'r', encoding='utf-8') as file:
            all_lines = file.readlines()
            recent_lines = all_lines[-lines:] if len(all_lines) > lines else all_lines
            print(f"\n最近{len(recent_lines)}条日志：")
            for line in recent_lines:
                print(line.strip())
    except FileNotFoundError:
        print("日志文件不存在")

# 使用示例
write_log("应用程序启动")
write_log("用户登录成功", "INFO")
write_log("数据处理完成", "SUCCESS")
write_log("发现警告信息", "WARNING")

read_recent_logs(lines=5)

def read_config(filename='config.ini'):
    """读取配置文件"""
    config = {}
    try:
        with open(filename, 'r', encoding='utf-8') as file:
            for line in file:
                line = line.strip()
                if line and not line.startswith('#'):  # 跳过空行和注释
                    key, value = line.split('=', 1)
                    config[key.strip()] = value.strip()
    except FileNotFoundError:
        print("配置文件不存在")
    return config

def write_config(config, filename='config.ini'):
    """写入配置文件"""
    with open(filename, 'w', encoding='utf-8') as file:
        file.write("# 应用程序配置\n\n")
        for key, value in config.items():
            file.write(f"{key} = {value}\n")
    print("配置已保存")

# 使用示例
app_config = {
    'database_host': 'localhost',
    'database_port': '5432',
    'database_name': 'myapp',
    'debug_mode': 'True',
    'max_connections': '100'
}

write_config(app_config)
loaded_config = read_config()

print("\n当前配置：")
for key, value in loaded_config.items():
    print(f"{key}: {value}")

def safe_file_operation(filename, operation='read'):
    """安全的文件操作"""
    try:
        if operation == 'read':
            with open(filename, 'r', encoding='utf-8') as file:
                return file.read()
        elif operation == 'write':
            # 这里可以添加写入逻辑
            pass
    except FileNotFoundError:
        print(f"错误：文件 {filename} 不存在")
    except PermissionError:
        print(f"错误：没有权限访问文件 {filename}")
    except UnicodeDecodeError:
        print(f"错误：文件编码问题")
    except Exception as e:
        print(f"未知错误：{e}")
    return None

# 使用示例
content = safe_file_operation('example.txt')
if content:
    print("文件内容：", content)

# 好的做法
with open('data.txt', 'r', encoding='utf-8') as file:
    for line in file:
        process_line(line)  # 逐行处理大文件

# 不好的做法
file = open('data.txt', 'r')
content = file.read()  # 可能内存溢出
file.close()