# TD-046MediumRuntime

The Retry Loop That Swallowed the Reason

bare except: pass hides the real failure

Published Oct 29, 2026

Executive Summary

A vibe-coded payment retry loop wraps the charge in bare except: pass. It never crashes — but it also never learns why the charge failed. A one-character typo and a gateway outage produce the same silent outcome: three attempts, then None, with nothing logged.

The Prompt

“Add error handling around the payment retry loop so it never crashes.”

The Flaw

bare except: pass swallows every exception — the real gateway error, but also typos, AttributeErrors, and KeyboardInterrupt. The loop never crashes, but it also never learns why the charge failed: a coding bug is indistinguishable from a provider outage. After three attempts it returns None, and the order silently fails with nothing in the logs to diagnose it.

Risk & Impact

[Correctness] Payments fail silently. A one-character typo in gateway.charge produces the same outcome as a provider outage — and there is no log to tell them apart.

Cost: Undiagnosable payment failures that only surface as angry customers and unprocessed orders.

Code Comparison

❌ Vulnerable (AI generated)

payment.pypython

def retry_payment(order):

for attempt in range(3):

try:

return gateway.charge(order)

except:

pass # swallow everything, try again

return None

❌ Vulnerable (AI generated)

payment.pypython

def retry_payment(order):

for attempt in range(3):

try:

return gateway.charge(order)

except:

pass # swallow everything, try again

return None

✅ Hardened (production ready)

payment.pypython

import logging

def retry_payment(order):

for attempt in range(3):

try:

return gateway.charge(order)

except gateway.TransientError as err: # retry only transient failures

logging.warning("charge attempt %d failed: %s", attempt + 1, err)

continue

raise RuntimeError("payment failed after 3 attempts")

The Fix

Catch the specific, retryable exception type — log it — and raise loudly when retries are exhausted. Never bare except, never pass.

Prevention

[linter] flake8-bugbear (B001) and pylint (W0702/W0703) flag bare except and except: pass.
[ci] A test that raises a non-transient error must NOT be retried and must raise — proving the loop only retries what it should.
[manual] Define the failure mode for each except clause (rule 2): what is retryable, what is fatal, and where the log goes.

Why This Happened

Root cause: the prompt omitted Rule 2 — the guardrails that would have caught this. See the full guide →

Sources

https://docs.python.org/3/tutorial/errors.html

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