How to implement retry mechanism into python requests library?

I would like to add a retry mechanism to python request library, so scripts that are using it will retry for non fatal errors.

At this moment I do consider three kind of errors to be recoverable:

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

At the first stage I do want to retry specified 5xx requests every minute.

I want to be able to add this functionality transparently, without having to manually implement recovery for each HTTP call made from inside these scripts or libraries that are using python-requests.

Solution 1:

This snippet of code will make all HTTP requests from the same session retry for a total of 5 times, sleeping between retries with an increasing backoff of 0s, 2s, 4s, 8s, 16s (the first retry is done immediately). It will retry on basic connectivity issues (including DNS lookup failures), and HTTP status codes of 502, 503 and 504.

import logging
import requests

from requests.adapters import HTTPAdapter, 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")

See Retry class for details.

Solution 2:

This is a snippet of code I used to retry for the petitions made with urllib2. Maybe you could use it for your 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 waiting time grows incrementally to avoid be banned from server.

Solution 3:

Possible solution using retrying package

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')

Solution 4:

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


MAX_RETRY = 2
MAX_RETRY_FOR_SESSION = 2
BACK_OFF_FACTOR = 0.3
TIME_BETWEEN_RETRIES = 1000
ERROR_CODES = (500, 502, 504)


def requests_retry_session(retries=MAX_RETRY_FOR_SESSION,
    back_off_factor=BACK_OFF_FACTOR,
    status_force_list=ERROR_CODES, 
    session=None):
       session = session  
       retry = Retry(total=retries, read=retries, connect=retries,
                     backoff_factor=back_off_factor,
                     status_forcelist=status_force_list,
                     method_whitelist=frozenset(['GET', 'POST']))
       adapter = HTTPAdapter(max_retries=retry)
       session.mount('http://', adapter)
       session.mount('https://', adapter)
       return session



class ConfigService:

   def __init__(self):
      self.session = requests_retry_session(session=requests.Session())

   def call_to_api():
      config_url = 'http://localhost:8080/predict/'
      headers = {
        "Content-Type": "application/json",
        "x-api-key": self.x_api_key
      } 
      response = self.session.get(config_url, headers=headers)
      return response