Using Python decorators to retry request

Question

I have multiple functions in my script which does a REST API api requests.As i need to handle the error scenarios i have put a retry mechanism as below.

no_of_retries = 3
def check_status():
    for i in range(0,no_of_retries):
        url = "http://something/something"
        try:
            result = requests.get(url, auth=HTTPBasicAuth(COMMON_USERNAME, COMMON_PASSWORD)).json()
            if 'error' not in result:
                return result
            else:
                continue
        except Exception as e:
            continue
    return None

I have several different methods which does similar operation. How can we do it better way to avoid duplication may be using decorators.

Answer 1

if you do not mind installing a library you could use the tenacity (github.com/jd/tenacity) module. one of their examples:

import random
from tenacity import retry, stop_after_attempt

# @retry  # retry forever
@retry(stop=stop_after_attempt(3))
def do_something_unreliable():
    if random.randint(0, 10) > 1:
        raise IOError("Broken sauce, everything is hosed!!!111one")
    else:
        return "Awesome sauce!"

print(do_something_unreliable())

this also allows you to specify the number of tries or seconds you want to keep retrying.

for your case this might look something like this (not tested!):

@retry(stop=stop_after_attempt(3))
def retry_get():
    result = requests.get(
            url, auth=HTTPBasicAuth(COMMON_USERNAME, COMMON_PASSWORD)).json()
    if 'error' not in result:
        raise RequestException(result)

Answer 2

You can use a decorator like this and handle your own exception.

def retry(times, exceptions):
    """
    Retry Decorator
    Retries the wrapped function/method `times` times if the exceptions listed
    in ``exceptions`` are thrown
    :param times: The number of times to repeat the wrapped function/method
    :type times: Int
    :param Exceptions: Lists of exceptions that trigger a retry attempt
    :type Exceptions: Tuple of Exceptions
    """
    def decorator(func):
        def newfn(*args, **kwargs):
            attempt = 0
            while attempt < times:
                try:
                    return func(*args, **kwargs)
                except exceptions:
                    print(
                        'Exception thrown when attempting to run %s, attempt '
                        '%d of %d' % (func, attempt, times)
                    )
                    attempt += 1
            return func(*args, **kwargs)
        return newfn
    return decorator

@retry(times=3, exceptions=(ValueError, TypeError))
def foo1():
    print('Some code here ....')
    print('Oh no, we have exception')
    raise ValueError('Some error')

foo1()