在请求中传递标头的效果？

我想知道当你传递标题时会有什么不同requests.get即之间的差异requests.get(url, headers) and requests.get(url).

我有这两段代码：

from lxml import html
from lxml import etree
import requests
import re

url = "http://www.amazon.in/SanDisk-micro-USB-connector-OTG-enabled-Android/dp/B00RBGYGMO"

page = requests.get(url)
tree = html.fromstring(page.text)
XPATH_IMAGE_SOURCE = '//*[@id="main-image-container"]//img/@src'
image_source = tree.xpath(XPATH_IMAGE_SOURCE)
print 'type: ',type(image_source[0])
print image_source[0]

正如您所期望的，它的输出是一个 url。但是这个：

from lxml import html
from lxml import etree
import requests
import re

url = "http://www.amazon.in/SanDisk-micro-USB-connector-OTG-enabled-Android/dp/B00RBGYGMO"
headers = {'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36'}
page = requests.get(url, headers=headers)

tree = html.fromstring(page.text)
XPATH_IMAGE_SOURCE = '//*[@id="main-image-container"]//img/@src'
image_source = tree.xpath(XPATH_IMAGE_SOURCE)
print 'type: ',type(image_source[0])
print image_source[0]

有一个以开头的输出data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAoHBwgHBgoIC我猜这是没有渲染的实际图像，只是纯数据。知道如何将其保留为 url 形式吗？标头的存在还会以哪些其他方式影响我们得到的响应？

谢谢

Save the first code's response to html file and open in your browser:

正如你所看到的，你被亚马逊禁止没有标题。

使用这个xpath：

XPATH_IMAGE_SOURCE = '//*[@id="main-image-container"]//img/@data-old-hires'

out:

type:  <class 'lxml.etree._ElementStringResult'>
http://ecx.images-amazon.com/images/I/617TjMIouyL._SL1274_.jpg

这是原始的 html 数据：

<img alt=".." src="&#10;data:image/webp;base64,UklGRuYIAABXRUJQVlA4INoIAACQQQCdASosAcsAPrFWpEqkIqQhIxN6gIgWCek6r4bUf/..." 
data-old-hires="http://ecx.images-amazon.com/images/I/617TjMIouyL._SL1274_.jpg"

图片网址在data-old-hires属性。