Python文件读写操作详解

发布时间: 2025-03-24 13:21

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# Python文件读写操作详解

本文将详细介绍Python中的文件读写操作,帮助你掌握文件处理的基本技能。

## 文件操作基础

### 打开文件

在Python中,使用`open()`函数打开文件：

```python
# 基本语法
file = open('filename', 'mode', encoding='encoding')

# 常用打开模式
# 'r': 只读模式(默认)
# 'w': 写入模式(会覆盖原有内容)
# 'a': 追加模式
# 'x': 独占写入模式
# 'b': 二进制模式
# '+': 读写模式

# 示例
file = open('test.txt', 'r', encoding='utf-8')
```

### 关闭文件

```python
# 手动关闭
file.close()

# 使用with语句(推荐)
with open('test.txt', 'r') as file:
    content = file.read()
# 文件会自动关闭
```

## 文件读取操作

### 读取整个文件

```python
# 读取所有内容
with open('test.txt', 'r') as file:
    content = file.read()
    print(content)

# 读取指定字节数
with open('test.txt', 'r') as file:
    content = file.read(10)  # 读取前10个字符
    print(content)
```

### 逐行读取

```python
# 读取单行
with open('test.txt', 'r') as file:
    line = file.readline()
    print(line)

# 读取所有行到列表
with open('test.txt', 'r') as file:
    lines = file.readlines()
    for line in lines:
        print(line.strip())  # strip()去除换行符

# 直接遍历文件对象
with open('test.txt', 'r') as file:
    for line in file:
        print(line.strip())
```

## 文件写入操作

### 写入文本

```python
# 写入字符串
with open('test.txt', 'w') as file:
    file.write('Hello, World!\n')
    file.write('Python文件操作\n')

# 写入多行
lines = ['第一行\n', '第二行\n', '第三行\n']
with open('test.txt', 'w') as file:
    file.writelines(lines)
```

### 追加内容

```python
# 追加模式
with open('test.txt', 'a') as file:
    file.write('追加的内容\n')
```

## 文件指针操作

### 移动文件指针

```python
# seek()方法
with open('test.txt', 'r') as file:
    # 移动到文件开头
    file.seek(0)
    
    # 移动到指定位置
    file.seek(10)
    
    # 获取当前位置
    position = file.tell()
    print(f'当前位置: {position}')
```

## 二进制文件操作

### 读取二进制文件

```python
# 读取图片文件
with open('image.jpg', 'rb') as file:
    data = file.read()
    print(f'文件大小: {len(data)} 字节')

# 分块读取大文件
def read_in_chunks(file_path, chunk_size=1024):
    with open(file_path, 'rb') as file:
        while True:
            chunk = file.read(chunk_size)
            if not chunk:
                break
            yield chunk

# 使用示例
for chunk in read_in_chunks('large_file.bin'):
    process_chunk(chunk)  # 处理数据块
```

### 写入二进制文件

```python
# 写入二进制数据
data = bytes([65, 66, 67, 68])  # ASCII: ABCD
with open('binary.bin', 'wb') as file:
    file.write(data)

# 复制文件
def copy_file(src_path, dst_path, chunk_size=1024):
    with open(src_path, 'rb') as src, open(dst_path, 'wb') as dst:
        while True:
            chunk = src.read(chunk_size)
            if not chunk:
                break
            dst.write(chunk)
```

## 实际应用示例

### 1. 日志记录器

```python
from datetime import datetime

class Logger:
    def __init__(self, filename):
        self.filename = filename
    
    def log(self, message, level='INFO'):
        timestamp = datetime.now().strftime('%Y-%m-%d %H:%M:%S')
        log_message = f'[{timestamp}] {level}: {message}\n'
        
        with open(self.filename, 'a') as file:
            file.write(log_message)
    
    def clear_log(self):
        with open(self.filename, 'w') as file:
            file.write('')  # 清空文件

# 使用示例
logger = Logger('app.log')
logger.log('应用程序启动')
logger.log('发生错误', 'ERROR')
```

### 2. 配置文件处理

```python
class ConfigParser:
    def __init__(self, filename):
        self.filename = filename
        self.config = {}
    
    def load(self):
        try:
            with open(self.filename, 'r') as file:
                for line in file:
                    line = line.strip()
                    if line and not line.startswith('#'):
                        key, value = line.split('=', 1)
                        self.config[key.strip()] = value.strip()
        except FileNotFoundError:
            print(f'配置文件 {self.filename} 不存在')
    
    def get(self, key, default=None):
        return self.config.get(key, default)
    
    def set(self, key, value):
        self.config[key] = value
    
    def save(self):
        with open(self.filename, 'w') as file:
            for key, value in self.config.items():
                file.write(f'{key}={value}\n')

# 使用示例
config = ConfigParser('config.ini')
config.load()
print(config.get('database_host', 'localhost'))
config.set('database_port', '5432')
config.save()
```

### 3. CSV文件处理

```python
class CSVHandler:
    def __init__(self, filename):
        self.filename = filename
    
    def read_csv(self):
        data = []
        with open(self.filename, 'r') as file:
            # 跳过标题行
            headers = file.readline().strip().split(',')
            
            # 读取数据行
            for line in file:
                values = line.strip().split(',')
                row = dict(zip(headers, values))
                data.append(row)
        return data
    
    def write_csv(self, data, headers=None):
        with open(self.filename, 'w') as file:
            # 写入标题行
            if headers:
                file.write(','.join(headers) + '\n')
            
            # 写入数据行
            for row in data:
                if isinstance(row, dict):
                    # 字典格式数据
                    values = [str(row.get(h, '')) for h in headers]
                else:
                    # 列表格式数据
                    values = [str(v) for v in row]
                file.write(','.join(values) + '\n')

# 使用示例
csv_handler = CSVHandler('data.csv')

# 写入数据
headers = ['name', 'age', 'city']
data = [
    {'name': 'Alice', 'age': '25', 'city': 'Beijing'},
    {'name': 'Bob', 'age': '30', 'city': 'Shanghai'}
]
csv_handler.write_csv(data, headers)

# 读取数据
read_data = csv_handler.read_csv()
for row in read_data:
    print(row)
```

## 最佳实践

1. **始终使用with语句**
```python
# 不好的做法
file = open('file.txt', 'r')
try:
    content = file.read()
finally:
    file.close()

# 好的做法
with open('file.txt', 'r') as file:
    content = file.read()
```

2. **指定正确的编码**
```python
# 不好的做法
with open('file.txt', 'r') as file:
    content = file.read()

# 好的做法
with open('file.txt', 'r', encoding='utf-8') as file:
    content = file.read()
```

3. **大文件处理**
```python
# 不好的做法
with open('large_file.txt', 'r') as file:
    content = file.read()  # 读取整个文件到内存

# 好的做法
with open('large_file.txt', 'r') as file:
    for line in file:  # 逐行处理
        process_line(line)
```

4. **异常处理**
```python
# 不好的做法
with open('file.txt', 'r') as file:
    content = file.read()

# 好的做法
try:
    with open('file.txt', 'r') as file:
        content = file.read()
except FileNotFoundError:
    print('文件不存在')
except PermissionError:
    print('没有读取权限')
except Exception as e:
    print(f'发生错误: {e}')
```

通过本文的学习,你应该已经掌握了Python文件操作的基本知识和实际应用方法。文件操作是编程中的重要基础,合理使用这些操作可以帮助你更好地处理数据和构建应用程序。继续练习和探索,你会发现更多文件操作的应用场景！

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