How to implement retry mechanism in python query library?

Question

I would like to add a retry mechanism to the Python query library so that the scripts that use it will retry when non-fatal errors occur.

At the moment, I consider three kinds of errors that can be fixed:

• HTTP return codes 502, 503, 504
• host not found (now this is less important)
• request timeout

In the first step, I want to repeat the indicated 5xx requests every minute.

I want to be able to transparently add this functionality, without having to manually restore each HTTP call from these scripts or libraries that use Python requests.

Answer 1

requests.Session requests.Session.

https://bitbucket.org/bspeakmon/jira-python/src/a7fca855394402f58507ca4056de87ccdbd6a213/jira/resilientsession.py?at=master

:

from requests import Session
from requests.exceptions import ConnectionError
import logging
import time


class ResilientSession(Session):

    """
    This class is supposed to retry requests that do return temporary errors.

    At this moment it supports: 502, 503, 504
    """

    def __recoverable(self, error, url, request, counter=1):
        if hasattr(error,'status_code'):
            if error.status_code in [502, 503, 504]:
                error = "HTTP %s" % error.status_code
            else:
                return False
        DELAY = 10 * counter
        logging.warn("Got recoverable error [%s] from %s %s, retry #%s in %ss" % (error, request, url, counter, DELAY))
        time.sleep(DELAY)
        return True


    def get(self, url, **kwargs):
        counter = 0
        while True:
            counter += 1
            try:
                r = super(ResilientSession, self).get(url, **kwargs)
            except ConnectionError as e:
                r = e.message
            if self.__recoverable(r, url, 'GET', counter):
                continue
            return r

    def post(self, url, **kwargs):
        counter = 0
        while True:
            counter += 1
            try:
                r = super(ResilientSession, self).post(url, **kwargs)
            except ConnectionError as e:
                r = e.message
            if self.__recoverable(r, url, 'POST', counter):
                continue
            return r

    def delete(self, url, **kwargs):
        counter = 0
        while True:
            counter += 1
            try:
                r = super(ResilientSession, self).delete(url, **kwargs)
            except ConnectionError as e:
                r = e.message
            if self.__recoverable(r, url, 'DELETE', counter):
                continue
            return r

    def put(self, url, **kwargs):
        counter = 0
        while True:
            counter += 1
            try:
                r = super(ResilientSession, self).put(url, **kwargs)
            except ConnectionError as e:
                r = e.message

            if self.__recoverable(r, url, 'PUT', counter):
                continue
            return r

    def head(self, url, **kwargs):
        counter = 0
        while True:
            counter += 1
            try:
                r = super(ResilientSession, self).head(url, **kwargs)
            except ConnectionError as e:
                r = e.message
            if self.__recoverable(r, url, 'HEAD', counter):
                continue
            return r

    def patch(self, url, **kwargs):
        counter = 0
        while True:
            counter += 1
            try:
                r = super(ResilientSession, self).patch(url, **kwargs)
            except ConnectionError as e:
                r = e.message

            if self.__recoverable(r, url, 'PATCH', counter):
                continue
            return r

    def options(self, url, **kwargs):
        counter = 0
        while True:
            counter += 1
            try:
                r = super(ResilientSession, self).options(url, **kwargs)
            except ConnectionError as e:
                r = e.message

            if self.__recoverable(r, url, 'OPTIONS', counter):
                continue
            return r

Answer 2

HTTP- 5 , 0, 2, 4, 8, 16 ( ). ( DNS), HTTP 502, 503 504.

import logging
import requests

from requests.adapters import HTTPAdapter
from requests.packages.urllib3.util.retry import Retry

logging.basicConfig(level=logging.DEBUG)

s = requests.Session()
retries = Retry(total=5, backoff_factor=1, status_forcelist=[ 502, 503, 504 ])
s.mount('http://', HTTPAdapter(max_retries=retries))

s.get("http://httpstat.us/503")

Retry class .

Answer 3

This is the code snippet that I used for retries made with urllib2. Perhaps you could use it for your own purposes:

retries = 1
success = False
while not success:
    try:
        response = urllib2.urlopen(request)
        success = True
    except Exception as e:
        wait = retries * 30;
        print 'Error! Waiting %s secs and re-trying...' % wait
        sys.stdout.flush()
        time.sleep(wait)
        retries += 1

The latency is increased gradually to avoid a ban on the server.

Answer 4

Possible solution using re-batch

from retrying import retry
import requests


def retry_if_connection_error(exception):
    """ Specify an exception you need. or just True"""
    #return True
    return isinstance(exception, ConnectionError)

# if exception retry with 2 second wait  
@retry(retry_on_exception=retry_if_connection_error, wait_fixed=2000)
def safe_request(url, **kwargs):
    return requests.get(url, **kwargs)

response = safe_request('test.com')

Answer 5

This is mainly logic in Java. You can try to look at it. Works fine.

public int callAPI() {
    return 1; //some method to be retried
}

public int retrylogic()  throws InterruptedException, IOException{
    int retry = 0;
    int status = -1;
    boolean delay = false;
    do {
        if (delay) {
            Thread.sleep(2000);
        }

        try {
            status = callAPI();
        }
        catch (Exception e) {
            System.out.println("Error occured");
            status = -1;
        }
        finally {
            switch (status) {
            case 200:
                System.out.println(" **OK**");
                return status; 
            default:
                System.out.println(" **unknown response code**.");
                break;
            }
            retry++;
            System.out.println("Failed retry " + retry + "/" + 3);
            delay = true;

        } 
    }while (retry < 3);

    return status;
}