Python FTP/HTTP 檔案下載完整實作：ftplib、urllib、requests 三種方案

方案一：ftplib（FTP 協定）

from ftplib import FTP
import os

def ftp_download(host, user, password, remote_path, local_path, port=21):
    with FTP() as ftp:
        ftp.connect(host, port, timeout=30)
        ftp.login(user, password)
        ftp.set_pasv(True)
        os.makedirs(os.path.dirname(local_path), exist_ok=True)
        with open(local_path, 'wb') as f:
            ftp.retrbinary(f'RETR {remote_path}', f.write, blocksize=8192)
    print(f"FTP 下載完成: {local_path}")

方案二：urllib.request（標準庫 HTTP/HTTPS）

import urllib.request
from datetime import datetime

def http_download_urllib(url, local_path):
    start = datetime.now()
    print(f"開始下載: {start}")
    
    req = urllib.request.Request(url, headers={'User-Agent': 'Mozilla/5.0'})
    with urllib.request.urlopen(req, timeout=60) as resp, open(local_path, 'wb') as f:
        # 可加入進度顯示
        total = int(resp.headers.get('Content-Length', 0))
        downloaded = 0
        block_size = 8192
        while True:
            chunk = resp.read(block_size)
            if not chunk:
                break
            f.write(chunk)
            downloaded += len(chunk)
            if total:
                print(f"\r進度: {downloaded/total*100:.1f}%", end='')
    
    elapsed = (datetime.now() - start).total_seconds()
    print(f"\n下載完成，耗時 {elapsed:.1f} 秒")

方案三：requests（第三方庫，推薦生產環境）

import requests
from datetime import datetime

def http_download_requests(url, local_path):
    start = datetime.now()
    print(f"開始下載: {start}")
    
    headers = {'User-Agent': 'Mozilla/5.0'}
    with requests.get(url, headers=headers, stream=True, timeout=60) as resp:
        resp.raise_for_status()
        total = int(resp.headers.get('Content-Length', 0))
        os.makedirs(os.path.dirname(local_path), exist_ok=True)
        
        with open(local_path, 'wb') as f:
            for chunk in resp.iter_content(chunk_size=8192):
                if chunk:
                    f.write(chunk)
    
    elapsed = (datetime.now() - start).total_seconds()
    print(f"下載完成，耗時 {elapsed:.1f} 秒")

三方案比較

斷點續傳提示

• HTTP：使用 Range: bytes=start- 標頭，需伺服器支援
• FTP：使用 REST 指令設定起始位置
• 建議使用 requests + tqdm 進度條庫實作完整續傳邏輯