Mastering Elegant Retry Logic in Python with Tenacity

Network instability often causes request timeouts, making retry logic crucial for robust applications.

The third‑party library Tenacity offers a comprehensive solution for implementing retries in Python, handling scenarios such as when to retry, how many attempts, delay intervals, and post‑failure callbacks.

When should a retry be performed?

How many times to retry?

When to stop retrying?

What interval between retries?

Callback after retry failure?

Install Tenacity via pip:

$ pip install tenacity

1. Basic Unconditional Retry

Retry without any condition and without delay:

from tenacity import retry

@retry
def test_retry():
    print("Waiting for retry, no interval...")
    raise Exception

test_retry()

Retry with a fixed 2‑second wait before each attempt:

from tenacity import retry, wait_fixed

@retry(wait=wait_fixed(2))
def test_retry():
    print("Waiting for retry...")
    raise Exception

test_retry()

2. Setting Stop Conditions

Stop after a maximum number of attempts (e.g., 7):

from tenacity import retry, stop_after_attempt

@retry(stop=stop_after_attempt(7))
def test_retry():
    print("Waiting for retry...")
    raise Exception

test_retry()

Stop after a time limit (e.g., 10 seconds):

from tenacity import retry, stop_after_delay

@retry(stop=stop_after_delay(10))
def test_retry():
    print("Waiting for retry...")
    raise Exception

test_retry()

Combine both conditions (stop when either is met):

from tenacity import retry, stop_after_delay, stop_after_attempt

@retry(stop=(stop_after_delay(10) | stop_after_attempt(7)))
def test_retry():
    print("Waiting for retry...")
    raise Exception

test_retry()

3. Conditional Retry Triggers

Retry only on specific exceptions, such as request timeouts:

from requests import exceptions
from tenacity import retry, retry_if_exception_type

@retry(retry=retry_if_exception_type(exceptions.Timeout))
def test_retry():
    print("Waiting for retry...")
    raise exceptions.Timeout

test_retry()

Retry based on a custom result condition (e.g., function returns False):

from tenacity import retry, stop_after_attempt, retry_if_result

def is_false(value):
    return value is False

@retry(stop=stop_after_attempt(3), retry=retry_if_result(is_false))
def test_retry():
    return False

print(test_retry())

4. Reraising the Original Exception

By default Tenacity raises RetryError after exhausting retries; use reraise=True to propagate the original exception:

from tenacity import retry, stop_after_attempt

@retry(stop=stop_after_attempt(7), reraise=True)
def test_retry():
    print("Waiting for retry...")
    raise Exception

test_retry()

5. Adding a Callback After Final Failure

Execute a callback function when all retries fail, optionally returning the original result:

from tenacity import *

def return_last_value(retry_state):
    print("Executing callback")
    return retry_state.outcome.result()

def is_false(value):
    return value is False

@retry(stop=stop_after_attempt(3), retry_error_callback=return_last_value, retry=retry_if_result(is_false))
def test_retry():
    print("Waiting for retry...")
    return False

print(test_retry())