Sandilya Bhamidipati
Posted on July 11, 2018
Note to self
Thanks a ton to Peter Bengtsson
This will setup up a function which as a drop-in replacement to the requests.get call can let you make requests with retries.
import requests
from requests.adapters import HTTPAdapter
from requests.packages.urllib3.util.retry import Retry
def requests_retry_session(
retries=3,
backoff_factor=0.3,
status_forcelist=(500, 502, 504),
session=None,
):
session = session or requests.Session()
retry = Retry(
total=retries,
read=retries,
connect=retries,
backoff_factor=backoff_factor,
status_forcelist=status_forcelist,
)
adapter = HTTPAdapter(max_retries=retry)
session.mount('http://', adapter)
session.mount('https://', adapter)
return session
Some testing is always good.
t0 = time.time()
try:
response = requests_retry_session().get(
'http://httpbin.org/status/500',
)
except Exception as x:
print('It failed :(', x.__class__.__name__)
else:
print('It eventually worked', response.status_code)
finally:
t1 = time.time()
print('Took', t1 - t0, 'seconds')
Intuition
The algorithm for that backoff is documented here:
A backoff factor to apply between attempts after the second try (most errors are resolved immediately by a second try without a delay). urllib3 will sleep for: {backoff factor} * (2 ^ ({number of total retries} - 1)) seconds. If the backoff_factor is 0.1, then sleep() will sleep for [0.0s, 0.2s, 0.4s, ...] between retries. It will never be longer than Retry.BACKOFF_MAX. By default, backoff is disabled (set to 0).
Posted on July 11, 2018
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