Python:什么可能导致请求对象丢失属性？

Question

我试图确定为什么同一脚本在多次运行时会以不同方式处理我返回的 Response 对象？当脚本成功时，响应对象将作为 <class 'requests.models.Response'> 传递。 ，当它不成功时，它会丢失所有属性并作为 <type 'NoneType'> 传递我不知道怎么会这样？

其他详细信息:

我正在运行一个脚本，该脚本通过 API 登录和注销 Tableau Server使用 Python 2.7 和请求。该脚本正在通过与我们的数据箱的 SSH 连接运行，我得到了一些奇怪的结果。

如果第一次尝试发布请求不成功，它将失败，但需要 2 到 7 次尝试才能达到该点。

脚本:

import time
import requests
import sys
import xml.etree.ElementTree as ET


class TableauHook():

    def __init__(self):
        self.url = 'https://{server}.com/api/2.8/'
        self.username = 'username'
        self.password = 'password'
        self.name = 'datasource_name'
        self.auth_header = None
        self.sign_in = self._sign_in()


    def _sign_in(self):
        endpoint = 'auth/signin'
        payload = '<tsRequest><credentials name="{name}" password="{pw}" ><site contentUrl="" /></credentials></tsRequest>'.format(
            name=self.username, pw=self.password)
        # Request setup
        req = self.send_request(req_type='post', endpoint=endpoint, payload=payload)
        print('Returned req: ' + str(type(req)))


        if req.content:
            print('Sign in to Tableau: Success')
            response = ET.fromstring(req.content)

            # Parse and store request data
            self.token = response.find('.//t:credentials',
                                       namespaces={'t': "http://tableau.com/api"}).attrib['token']
            self.site_id = response.find('.//t:site',
                                         namespaces={'t': "http://tableau.com/api"}).attrib['id']
            self.auth_header = {'X-tableau-auth': self.token}

            print('Token: exists' )
            print('Site id: exists')
            print('Auth_header: exists' )
        else:
            print('Sign in to Tableau unsuccessful')


    def send_request(self, req_type, endpoint, payload=None, attempts=None):
        # Count attempts to send request
        if attempts == None:
            attempts = 1
        else:
            attempts = attempts

        if attempts > 20:
            sys.exit('Too many attempts made')

        print('\nAttempt: ' + str(attempts))
        print('Endpoint: ' + endpoint)
        # Send request/load response
        try:
            if req_type.upper() == 'POST':
                response = requests.post(self.url + endpoint, data=payload, headers=self.auth_header)
                print('Response: ' + str(type(response)))
                if type(response) == type(None):
                    print('Response is NoneType')
                    raise Exception('NoneType returned')
                return response
            elif req_type.upper() == 'GET':
                response = requests.get(self.url + endpoint, data=payload, headers=self.auth_header)
                print('Response: ' + str(type(response)))
                if type(response) == type(None):
                    raise Exception('NoneType returned')
                return response

        except Exception as e:
            print('Error: ' + str(e))
            print('Sleeping for 3 seconds...')
            time.sleep(3)
            attempts += 1
            print('Running send_request() again')
        self.send_request(req_type=req_type, endpoint=endpoint, payload=payload, attempts=attempts)



    def sign_out(self):
        endpoint = 'auth/signout'
        try:
            req = requests.post(self.url+endpoint, headers=self.auth_header)
        except Exception as e:
            print(e)
            time.sleep(3)
            req = requests.post(self.url + endpoint, headers=self.auth_header)
        print('Returned response: ' + str(type(req)))
        print(req)
        print('\n')

def main():
    hook = TableauHook()
    print('\nSigning out\n')
    hook.sign_out()


if __name__ == '__main__':
    main()

这是 2 次不同尝试的控制台输出:

# First attempt to run the script
[user@databox directory]$ python TableauDBTest.py 

Attempt: 1
Endpoint: auth/signin
Response: <class 'requests.models.Response'>
Returned req: <class 'requests.models.Response'>
Sign in to Tableau: Success
Token: exists
Site id: exists
Auth_header: exists

Signing out

Returned response: <class 'requests.models.Response'>
<Response [204]>

# Run the script again, this time with different results
[user@databox directory]$ python TableauDBTest.py 

Attempt: 1
Endpoint: auth/signin
Error: ('Connection aborted.', error(104, 'Connection reset by peer'))
Sleeping for 3 seconds...
Running send_request() again

Attempt: 2
Endpoint: auth/signin
Response: <class 'requests.models.Response'>
Returned req: <type 'NoneType'>
Traceback (most recent call last):
  File "TableauDBTest.py", line 115, in <module>
    main()
  File "TableauDBTest.py", line 109, in main
    hook = TableauHook()
  File "TableauDBTest.py", line 15, in __init__
    self.sign_in = self._sign_in()
  File "TableauDBTest.py", line 27, in _sign_in
    if req.content:
AttributeError: 'NoneType' object has no attribute 'content'

提前感谢您对可能导致此问题的任何想法!

Answer 1

您的 send_request 方法正在递归调用 self.send_request，但它没有返回值；它只是忽略它，然后从函数末尾掉下来并返回 None。

因此，最简单的解决方法是更改​​最后一行:

self.send_request(req_type=req_type, endpoint=endpoint, payload=payload, attempts=attempts)

…对此:

return self.send_request(req_type=req_type, endpoint=endpoint, payload=payload, attempts=attempts)

但是，将其重写为循环而不是使用递归会简单得多:

def send_request(self, req_type, endpoint, payload=None):
    for attempt in range(1, 21):
        print(etc.)
        try:
            stuff
            return response
        except blah blah:
            ...
    sys.exit('Too many attempts made')