# 传统方式 - 需要手动关闭
file = open('example.txt', 'r', encoding='utf-8')
content = file.read()
file.close()  # 忘记关闭会导致资源泄漏

# 推荐方式 - 使用 with 语句（自动关闭）
with open('example.txt', 'r', encoding='utf-8') as file:
    content = file.read()
    # 文件在 with 块结束后自动关闭

# 推荐使用 UTF-8 编码
with open('file.txt', 'r', encoding='utf-8') as f:
    content = f.read()

# 处理不同编码
with open('file.txt', 'r', encoding='gbk') as f:
    content = f.read()

# 遇到编码错误时的处理
with open('file.txt', 'r', encoding='utf-8', errors='ignore') as f:
    content = f.read()

with open('file.txt', 'r', encoding='utf-8', errors='replace') as f:
    content = f.read()  # 替换为 ?

# 读取整个文件
with open('example.txt', 'r', encoding='utf-8') as f:
    content = f.read()  # 返回字符串

# 读取前 N 个字符
with open('example.txt', 'r', encoding='utf-8') as f:
    content = f.read(100)  # 读取前100个字符

# 读取单行（包含换行符）
with open('example.txt', 'r', encoding='utf-8') as f:
    line1 = f.readline()
    line2 = f.readline()

# 读取所有行（返回列表）
with open('example.txt', 'r', encoding='utf-8') as f:
    lines = f.readlines()

# 直接迭代文件对象（推荐，内存高效）
with open('example.txt', 'r', encoding='utf-8') as f:
    for line in f:
        print(line.strip())  # strip() 去除换行符

with open('example.txt', 'r', encoding='utf-8') as f:
    while True:
        char = f.read(1)  # 读取单个字符
        if not char:
            break
        print(char, end='')

# 写入单行（不自动添加换行符）
with open('output.txt', 'w', encoding='utf-8') as f:
    f.write('第一行')
    f.write('第二行')  # 不会换行

# 写入多行
with open('output.txt', 'w', encoding='utf-8') as f:
    lines = ['第一行\n', '第二行\n', '第三行\n']
    f.writelines(lines)

# 使用 print 函数写入（自动添加换行符）
with open('output.txt', 'w', encoding='utf-8') as f:
    print('第一行', file=f)
    print('第二行', file=f)

# 在文件末尾追加
with open('log.txt', 'a', encoding='utf-8') as f:
    f.write('新的日志条目\n')

# 写入二进制数据
with open('data.bin', 'wb') as f:
    f.write(b'\x00\x01\x02\x03')

# 读取二进制数据
with open('data.bin', 'rb') as f:
    data = f.read()
    print(data)  # b'\x00\x01\x02\x03'

with open('example.txt', 'r', encoding='utf-8') as f:
    # 获取文件指针位置
    print(f.tell())  # 0
    
    # 读取一些内容
    content = f.read(10)
    print(f.tell())  # 10
    
    # 移动文件指针
    f.seek(0)        # 移到开头
    print(f.tell())  # 0
    
    f.seek(5)        # 移到第5个字节
    print(f.tell())  # 5
    
    # 从末尾往前移动（需要使用二进制模式）
    # f.seek(-10, 2)  # 从文件末尾往前10字节

import json

# Python 对象与 JSON 的对应关系：
# dict        ↔ object
# list/tuple  ↔ array
# str         ↔ string
# int/float   ↔ number
# True/None   ↔ true/null
# False       ↔ false

# 字典转 JSON 字符串
data = {'name': '张三', 'age': 25, 'city': '北京'}

# 转为字符串
json_str = json.dumps(data)
print(json_str)
# 输出: {"name": "\u5f20\u4e09", "age": 25, "city": "\u5317\u4eac"}

# 美化输出
json_str_pretty = json.dumps(data, indent=4, ensure_ascii=False)
print(json_str_pretty)

# 按键排序
json_str_sorted = json.dumps(data, sort_keys=True, ensure_ascii=False)
print(json_str_sorted)

# 处理特殊类型
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

# 自定义编码器
def person_encoder(obj):
    if isinstance(obj, Person):
        return {'name': obj.name, 'age': obj.age, 'type': 'Person'}
    raise TypeError(f"Object of type {type(obj)} is not JSON serializable")

person = Person('李四', 30)
json_str = json.dumps(person, default=person_encoder, ensure_ascii=False)
print(json_str)

# JSON 字符串转字典
json_str = '{"name": "张三", "age": 25}'
data = json.loads(json_str)
print(data)  # {'name': '张三', 'age': 25}

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

# 处理特殊解码
def person_decoder(dct):
    if 'type' in dct and dct['type'] == 'Person':
        return Person(dct['name'], dct['age'])
    return dct

json_str = '{"name": "王五", "age": 28, "type": "Person"}'
person = json.loads(json_str, object_hook=person_decoder)

# 写入 JSON 文件
data = {
    'users': [
        {'name': '张三', 'age': 25},
        {'name': '李四', 'age': 30}
    ],
    'count': 2
}

with open('users.json', 'w', encoding='utf-8') as f:
    json.dump(data, f, indent=4, ensure_ascii=False)

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

# 追加写入 JSON Lines 格式
with open('logs.jsonl', 'a', encoding='utf-8') as f:
    log_entry = {'timestamp': '2024-01-01', 'level': 'INFO', 'message': '系统启动'}
    f.write(json.dumps(log_entry, ensure_ascii=False) + '\n')

# 基本上下文管理器
with open('file.txt', 'r') as f:
    content = f.read()

# 多个文件
with open('input.txt', 'r') as infile, open('output.txt', 'w') as outfile:
    content = infile.read()
    outfile.write(content.upper())

# 自定义上下文管理器
class FileManager:
    def __init__(self, filename, mode):
        self.filename = filename
        self.mode = mode
        self.file = None
    
    def __enter__(self):
        self.file = open(self.filename, self.mode)
        return self.file
    
    def __exit__(self, exc_type, exc_val, exc_tb):
        if self.file:
            self.file.close()
        return False  # 不抑制异常

# 使用
with FileManager('test.txt', 'w') as f:
    f.write('Hello, World!')

# config.json
# {
#     "database": {
#         "host": "localhost",
#         "port": 3306,
#         "name": "myapp"
#     },
#     "app": {
#         "debug": true,
#         "secret_key": "abc123"
#     }
# }

import json
from pathlib import Path

class Config:
    def __init__(self, config_path='config.json'):
        self.config_path = Path(config_path)
        self.data = {}
    
    def load(self):
        """加载配置文件"""
        if self.config_path.exists():
            with open(self.config_path, 'r', encoding='utf-8') as f:
                self.data = json.load(f)
        else:
            print(f"配置文件 {self.config_path} 不存在，使用默认配置")
            self.data = self.get_default_config()
        return self
    
    def save(self):
        """保存配置到文件"""
        with open(self.config_path, 'w', encoding='utf-8') as f:
            json.dump(self.data, f, indent=4, ensure_ascii=False)
    
    @staticmethod
    def get_default_config():
        """获取默认配置"""
        return {
            'database': {
                'host': 'localhost',
                'port': 5432,
                'name': 'default_db',
                'user': 'admin',
                'password': 'admin'
            },
            'app': {
                'debug': False,
                'secret_key': 'change-me-in-production',
                'log_level': 'INFO'
            }
        }
    
    def get(self, key, default=None):
        """获取配置项（支持点号分隔的路径）"""
        keys = key.split('.')
        value = self.data
        for k in keys:
            if isinstance(value, dict):
                value = value.get(k)
                if value is None:
                    return default
            else:
                return default
        return value
    
    def set(self, key, value):
        """设置配置项"""
        keys = key.split('.')
        target = self.data
        for k in keys[:-1]:
            if k not in target:
                target[k] = {}
            target = target[k]
        target[keys[-1]] = value

# 使用示例
if __name__ == '__main__':
    config = Config('app_config.json')
    config.load()
    
    # 获取配置
    db_host = config.get('database.host')
    print(f"数据库主机: {db_host}")
    
    # 修改配置
    config.set('app.debug', True)
    config.save()

# A.
with open('file.txt', 'r') as f:
    content = f.read()

# B.
with open('file.txt', 'r') as f:
    lines = f.readlines()

# C.
with open('file.txt', 'r') as f:
    for line in f:
        print(line)

# D.
以上全部正确

# A. 'r+'
# B. 'w'
# C. 'a'
# D. 'x'

# A. 忽略所有 ASCII 字符
# B. 保留非 ASCII 字符（如中文）
# C. 将所有字符转为 ASCII
# D. 报错

# A. read() 一次性读取
# B. readlines() 读取到列表
# C. for line in file 迭代
# D. readline() 循环

# A. 移到文件开头
# B. 移到文件末尾
# C. 当前位置
# D. 下一行

def copy_file(src, dst):
    """复制文件"""
    with open(src, 'rb') as src_file:
        with open(dst, 'wb') as dst_file:
            # 分块复制（适合大文件）
            while chunk := src_file.read(8192):
                dst_file.write(chunk)
    print(f"已复制: {src} -> {dst}")

# 使用
copy_file('source.txt', 'destination.txt')

import json
from datetime import datetime

def append_log(log_file, level, message):
    """追加日志到 JSON Lines 文件"""
    log_entry = {
        'timestamp': datetime.now().isoformat(),
        'level': level,
        'message': message
    }
    with open(log_file, 'a', encoding='utf-8') as f:
        f.write(json.dumps(log_entry, ensure_ascii=False) + '\n')

def read_logs(log_file):
    """读取所有日志"""
    logs = []
    with open(log_file, 'r', encoding='utf-8') as f:
        for line in f:
            if line.strip():
                logs.append(json.loads(line))
    return logs

def filter_logs(log_file, level):
    """按级别过滤日志"""
    with open(log_file, 'r', encoding='utf-8') as f:
        for line in f:
            if line.strip():
                entry = json.loads(line)
                if entry['level'] == level:
                    yield entry

# 使用
append_log('app.log', 'INFO', '应用启动')
append_log('app.log', 'ERROR', '发生错误')
append_log('app.log', 'INFO', '处理完成')

# 读取所有日志
all_logs = read_logs('app.log')
print(f"共 {len(all_logs)} 条日志")

# 过滤错误日志
for log in filter_logs('app.log', 'ERROR'):
    print(f"[{log['timestamp']}] {log['message']}")

import json

class ConfigManager:
    """配置文件管理器"""
    
    def __init__(self, config_file='config.json'):
        self.config_file = config_file
        self.config = {}
        self.load()
    
    def load(self):
        """从文件加载配置"""
        try:
            with open(self.config_file, 'r', encoding='utf-8') as f:
                self.config = json.load(f)
        except FileNotFoundError:
            print(f"配置文件 {self.config_file} 不存在")
            self.config = self._default_config()
    
    def save(self):
        """保存配置到文件"""
        with open(self.config_file, 'w', encoding='utf-8') as f:
            json.dump(self.config, f, indent=4, ensure_ascii=False)
    
    @staticmethod
    def _default_config():
        """默认配置"""
        return {
            'version': '1.0.0',
            'database': {
                'host': 'localhost',
                'port': 3306,
                'name': 'testdb',
                'charset': 'utf8mb4'
            },
            'server': {
                'host': '0.0.0.0',
                'port': 8080,
                'debug': True
            },
            'logging': {
                'level': 'INFO',
                'file': 'app.log'
            }
        }
    
    def get(self, key_path):
        """获取配置项（支持路径如 'database.host'）"""
        keys = key_path.split('.')
        value = self.config
        for key in keys:
            if isinstance(value, dict):
                value = value.get(key)
            else:
                return None
        return value
    
    def set(self, key_path, value):
        """设置配置项"""
        keys = key_path.split('.')
        target = self.config
        for key in keys[:-1]:
            target = target.setdefault(key, {})
        target[keys[-1]] = value

# 使用示例
if __name__ == '__main__':
    config = ConfigManager('app_config.json')
    
    # 读取配置
    print(f"数据库主机: {config.get('database.host')}")
    print(f"服务器端口: {config.get('server.port')}")
    
    # 修改配置
    config.set('server.debug', False)
    config.set('database.host', '192.168.1.100')
    
    # 保存
    config.save()
    print("配置已保存")

# 常见编码处理
with open('file.txt', 'r', encoding='utf-8') as f:  # UTF-8
    pass

with open('file.txt', 'r', encoding='gbk') as f:    # GBK
    pass

# 错误处理
with open('file.txt', 'r', encoding='utf-8', errors='ignore') as f:   # 忽略错误
    pass

with open('file.txt', 'r', encoding='utf-8', errors='replace') as f: # 替换为 ?
    pass