使用 Python 从 REST URL 下载文件

使用 Python 从 REST URL 下载文件，可以使用 requests 库来简化文件的下载和保存过程。以下是一个示例代码，展示了如何从给定的 REST API 或 URL 下载文件并保存到本地。

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1、问题背景

我们需要编写一个脚本，从一个支持 REST URL 的网站下载一堆文件。该网站的 GET 请求如下：

GET /test/download/id/5774/format/testTitle HTTP/1.1
Host: testServer.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20100101 Firefox/23.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: __utma=11863783.1459862770.1379789243.1379789243.1379789243.1; __utmb=11863783.28.9.1379790533699; __utmc=11863783; __utmz=11863783.1379789243.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); PHPSESSID=fa844952890e9091d968c541caa6965f; loginremember=Qraoz3j%2BoWXxwqcJkgW9%2BfGFR0SDFLi1FLS7YVAfvbcd9GhX8zjw4u6plYFTACsRruZM4n%2FpX50%2BsjXW5v8vykKw2XNL0Vqo5syZKSDFSSX9mTFNd5KLpJV%2FFlYkCY4oi7Qyw%3D%3D; ma-refresh-storage=1; ma-pref=KLSFKJSJSD897897; skipPostLogin=0; pp-sid=hlh6hs1pnvuh571arl59t5pao0; __utmv=11863783.|1=MemberType=Yearly=1; nats_cookie=http%253A%252F%252Fwww.testServer.com%252F; nats=NDc1NzAzOjQ5MzoyNA%2C74%2C0%2C0%2C0; nats_sess=fe3f77e6e326eb8d18ef0111ab6f322e; __utma=163815075.1459708390.1379790355.1379790355.1379790355.1; __utmb=163815075.1.9.1379790485255; __utmc=163815075; __utmz=163815075.1379790355.1.1.utmcsr=ppp.contentdef.com|utmccn=(referral)|utmcmd=referral|utmcct=/postlogin; unlockedNetworks=%5B%22rk%22%2C%22bz%22%2C%22wkd%22%5D
Connection: close

如果请求成功，它将返回一个 302 响应，如下所示：

HTTP/1.1 302 Found
Date: Sat, 21 Sep 2013 19:32:37 GMT
Server: Apache
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
location: http://downloads.test.stuff.com/5774/stuff/picture.jpg?wed=20130921152237&wer=20130922153237&hash=0f20f4a6d0c9f1720b0b6
Vary: User-Agent,Accept-Encoding
Content-Length: 0
Connection: close
Content-Type: text/html; charset=UTF-8

我们需要做的是检查是否收到 302 响应。如果不是，则继续执行，如果是，则需要解析出这里显示的 location 参数：

location: http://downloads.test.stuff.com/5774/stuff/picture.jpg?wed=20130921152237&wer=20130922153237&hash=0f20f4a6d0c9f1720b0b6

拿到 location 参数后，我们需要向该 URL 发出另一个 GET 请求以下载文件。我们还需要在会话中维护 Cookie 以便下载文件。

2、解决方案

我们可以使用 requests 库来完成这个任务。requests 库是一个用于发送 HTTP 请求的库，它提供了多种方法来处理 HTTP 响应。

首先，我们需要安装 requests 库：

pip install requests

然后，我们可以使用 requests 库来发送 GET 请求：

import requests# 发送 GET 请求
response = requests.get("http://testServer.com/test/download/id/5774/format/testTitle",headers={"User-Agent": "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20100101 Firefox/23.0"},cookies={"__utma": "11863783.1459862770.1379789243.1379789243.1379789243.1","__utmb": "11863783.28.9.1379790533699","__utmc": "11863783","__utmz": "11863783.1379789243.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)","PHPSESSID": "fa844952890e9091d968c541caa6965f","loginremember": "Qraoz3j%2BoWXxwqcJkgW9%2BfGFR0SDFLi1FLS7YVAfvbcd9GhX8zjw4u6plYFTACsRruZM4n%2FpX50%2BsjXW5v8vykKw2XNL0Vqo5syZKSDFSSX9mTFNd5KLpJV%2FFlYkCY4oi7Qyw%3D%3D","ma-refresh-storage": "1","ma-pref": "KLSFKJSJSD897897","skipPostLogin": "0","pp-sid": "hlh6hs1pnvuh571arl59t5pao0","__utmv": "11863783.|1=MemberType=Yearly=1","nats_cookie": "http%253A%252F%252Fwww.testServer.com%252F","nats": "NDc1NzAzOjQ5MzoyNA%2C74%2C0%2C0%2C0","nats_sess": "fe3f77e6e326eb8d18ef0111ab6f322e","__utma": "163815075.1459708390.1379790355.1379790355.1379790355.1","__utmb": "163815075.1.9.1379790485255","__utmc": "163815075","__utmz": "1