通过FTP逐行读取CSV，而无需将整个文件存储在内存/磁盘中

import ftplib

def read_csv_via_ftp(host, username, password, filename):
    try:
        # 连接到FTP服务器
        ftp = ftplib.FTP(host)
        ftp.login(username, password)
        
        # 切换到二进制模式，以防文件包含特殊字符
        ftp.sendcmd('TYPE I')
        
        # 获取文件大小
        file_size = ftp.size(filename)
        
        # 打开一个文件句柄用于读取
        with open(filename, 'wb') as file:
            # 逐块下载文件
            block_size = 8192
            for i in range(0, file_size, block_size):
                block = ftp.retrbinary(f'RETR {filename}', file.write, blocksize=block_size)
        
        # 关闭FTP连接
        ftp.quit()
        
        # 逐行读取CSV文件
        with open(filename, 'r', encoding='utf-8') as csvfile:
            for line in csvfile:
                # 处理每一行数据
                process_line(line.strip())
                
    except Exception as e:
        print(f"Error: {e}")

def process_line(line):
    # 这里可以添加具体的处理逻辑
    print(line)

# 示例调用
read_csv_via_ftp('ftp.example.com', 'username', 'password', 'data.csv')