====== 第十八章：文件操作 ======

===== 本章目标 =====

完成本章学习后，你将能够：
  * 读写文本文件和二进制文件
  * 使用上下文管理器
  * 掌握文件系统操作
  * 处理CSV、JSON等格式

===== 文件读写基础 =====

==== 打开文件 ====

<code python>
# 基本语法
f = open('file.txt', 'r', encoding='utf-8')
content = f.read()
f.close()

# 使用with语句（推荐）
with open('file.txt', 'r', encoding='utf-8') as f:
    content = f.read()
# 自动关闭文件
</code>

==== 读取模式 ====

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

# 按行读取
with open('file.txt', 'r', encoding='utf-8') as f:
    for line in f:
        print(line.strip())

# 读取为列表
with open('file.txt', 'r', encoding='utf-8') as f:
    lines = f.readlines()

# 逐行读取（大文件）
with open('file.txt', 'r', encoding='utf-8') as f:
    while True:
        line = f.readline()
        if not line:
            break
        print(line.strip())
</code>

==== 写入模式 ====

<code python>
# 写入（覆盖）
with open('output.txt', 'w', encoding='utf-8') as f:
    f.write('Hello, World!\n')
    f.write('Second line\n')

# 追加
with open('log.txt', 'a', encoding='utf-8') as f:
    f.write('New log entry\n')

# 写入多行
lines = ['Line 1\n', 'Line 2\n', 'Line 3\n']
with open('output.txt', 'w', encoding='utf-8') as f:
    f.writelines(lines)
</code>

===== 文件系统操作 =====

<code python>
import os
import shutil

# 路径操作
print(os.path.join('folder', 'file.txt'))  # folder/file.txt
print(os.path.abspath('file.txt'))
print(os.path.dirname('/path/to/file.txt'))
print(os.path.basename('/path/to/file.txt'))
print(os.path.splitext('file.txt'))  # ('file', '.txt')

# 文件/目录操作
os.mkdir('new_folder')           # 创建目录
os.makedirs('a/b/c', exist_ok=True)  # 递归创建
os.remove('file.txt')            # 删除文件
os.rmdir('empty_folder')         # 删除空目录
shutil.rmtree('folder')          # 删除目录及内容
shutil.copy('src.txt', 'dst.txt')    # 复制文件
shutil.move('src.txt', 'dst/')       # 移动文件

# 遍历目录
for root, dirs, files in os.walk('.'):
    for file in files:
        print(os.path.join(root, file))
</code>

===== 处理不同文件格式 =====

==== JSON ====

<code python>
import json

data = {'name': 'Alice', 'age': 25, 'hobbies': ['reading', 'coding']}

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

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

# 字符串转换
json_str = json.dumps(data, indent=2)
parsed = json.loads(json_str)
</code>

==== CSV ====

<code python>
import csv

# 写入CSV
with open('data.csv', 'w', newline='', encoding='utf-8') as f:
    writer = csv.writer(f)
    writer.writerow(['Name', 'Age', 'City'])
    writer.writerow(['Alice', 25, 'NYC'])
    writer.writerow(['Bob', 30, 'LA'])

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

# 字典方式
with open('data.csv', 'r', encoding='utf-8') as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(row['Name'], row['Age'])
</code>

===== 本章练习 =====

1. 实现文件复制工具
2. 实现日志文件分析器
3. 实现目录同步工具
4. 实现配置文件管理器

下一章：[[python_course:chapter19|第十九章：异常处理]]