tenacity 9.1.4: Retry a flaky call with backoff and give up on the errors that will never succeed

{"case":{"caseId":"case:sha256:e95b2d65f45ae3869f087aecfeddb905091f9762f83d3fa54d854f75fc95257a","constraints":{"runtime":"python"},"contract":["retry a function that fails twice then succeeds","assert it was called exactly three times","assert an exception type outside the retry filter is raised immediately","assert exhausting the attempts raises RetryError carrying the last failure"],"goal":"Retry a flaky call with backoff and give up on the errors that will never succeed","kind":"HOW","packages":["pkg:pypi/tenacity@9.1.4"],"schemaVersion":1,"symbols":["retry","stop_after_attempt","wait_fixed","retry_if_exception_type"]},"contractCommand":["python","test/contract.py"],"environment":{"arch":"x64","ecosystem":"pypi","executionContext":"python","language":"python","os":"linux","packageManager":"pip","runtime":"python","runtimeVersion":"3.12","schemaVersion":1},"license":"MIT-0","packages":["pkg:pypi/tenacity@9.1.4"],"schemaVersion":1,"symbols":["retry","stop_after_attempt","wait_fixed","retry_if_exception_type"],"verifierAdapter":"python@1"}

tenacity==9.1.4

"""Bounded retries with tenacity."""

from tenacity import (
    retry,
    retry_if_exception_type,
    stop_after_attempt,
    wait_fixed,
)


class Transient(Exception):
    """Worth retrying: a timeout, a 503, a dropped connection."""


class Permanent(Exception):
    """Never worth retrying: bad credentials, a 400, a missing table."""


def make_flaky(fail_times, error=Transient):
    calls = {"n": 0}

    @retry(
        # Without retry=, tenacity retries EVERY exception, which turns a
        # permanent failure into the same failure N times and N times slower.
        retry=retry_if_exception_type(Transient),
        stop=stop_after_attempt(3),
        wait=wait_fixed(0.01),
    )
    def call():
        calls["n"] += 1
        if calls["n"] <= fail_times:
            raise error("attempt %d" % calls["n"])
        return "ok"

    return call, calls

import os
import sys

sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
from tenacity import RetryError

from src.retry import Permanent, Transient, make_flaky

# Fails twice, succeeds on the third attempt.
call, calls = make_flaky(2)
assert call() == "ok"
assert calls["n"] == 3, calls

# A permanent error is not retried: raised on the first attempt.
call, calls = make_flaky(5, error=Permanent)
try:
    call()
except Permanent:
    pass
else:
    raise AssertionError("a non-retryable error must propagate immediately")
assert calls["n"] == 1, calls

# Exhausting the attempts raises RetryError wrapping the last failure.
call, calls = make_flaky(99)
try:
    call()
except RetryError as exc:
    assert calls["n"] == 3, calls
    assert isinstance(exc.last_attempt.exception(), Transient)
else:
    raise AssertionError("exhausted retries must raise RetryError")

print("CONTRACT PASS: tenacity retried only what it was told to, three times")