TimedOut is a subclass of NetworkError in python-telegram-bot. The
inner retry loop in send() and the outer _send_with_retry() in base.py
both treated it as a transient connection error and retried — but
send_message is not idempotent. When the request reaches Telegram but
the HTTP response times out, the message is already delivered. Retrying
sends duplicates. Worst case: up to 9 copies (inner 3x × outer 3x).
Inner loop (telegram.py):
- Import TimedOut separately, isinstance-check before generic
NetworkError retry (same pattern as BadRequest carve-out from #3390)
- Re-raise immediately — no retry
- Mark as retryable=False in outer exception handler
Outer loop (base.py):
- Remove 'timeout', 'timed out', 'readtimeout', 'writetimeout' from
_RETRYABLE_ERROR_PATTERNS (read/write timeouts are delivery-ambiguous)
- Add 'connecttimeout' (safe — connection never established)
- Keep 'network' (other platforms still need it)
- Add _is_timeout_error() + early return to prevent plain-text fallback
on timeout errors (would also cause duplicate delivery)
Connection errors (ConnectionReset, ConnectError, etc.) are still
retried — these fail before the request reaches the server.
Credit: tmdgusya (PR #3899), barun1997 (PR #3904) for identifying the
bug and proposing fixes.
Closes#3899, closes#3904.
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