Python 新手，有个很奇怪的问题，特来请教

import urllib.request
import urllib.parse

url = 'http://fanyi.youdao.com/translate?smartresult=dict&smartresult=rule&smartresult=ugc&sessionFrom=null'
data = {}
data['i'] = 'love'
data['from'] = 'AUTO'
data['to'] = 'AUTO'
data['smartresult'] = 'dict'
data['client'] = 'fanyideskweb'
data['salt'] = '1502634572544'
#sign:50b0d2d06c1220f996cc3766c05fca1c 会变
data['doctype'] = 'json'
data['version'] = '2.1'
data['keyfrom'] = 'fanyi.web'
data['action'] = 'FY_BY_CLlCKBUTTON'
data['typoResult'] = 'true'
data = urllib.parse.urlencode(data).encode('utf-8')

req = urllib.request.Request(url,data)
req.add_header('Referer','http://fanyi.youdao.com')
req.add_header('User-Agent','Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Safari/537.36')
response = urllib.request.urlopen(req)
html = response.read().decode('utf-8')
print(html)
其中第三行代码（ url 这一行）我换成
http://fanyi.youdao.com/translate?smartresult=dict&smartresult=rule&smartresult=ugc&sessionFrom=null
就可以爬取，但是换成直接从网页上复制下来的
http://fanyi.youdao.com/translate_o?smartresult=dict&smartresult=rule&sessionFrom=
就不可以，这是为什么啊？还有就是我注释掉的这一行是什么意思，翻译时每次都会变。