Telethon development

Telethon Development Patterns

Production patterns and gotchas for the Telethon Telegram MTProto client library.

When to Use

• Debugging FloodWaitError, account bans, or flood wait cycling
• Mocking Telethon clients for unit/integration tests
• Storing Telethon data in a database (boolean normalization, serialization)
• Resolving/normalizing chat IDs before DB storage
• Handling new or version-specific Telethon types

When NOT to Use

• Bot API (python-telegram-bot) — different library, different patterns
• Telethon v2 — major API changes; verify patterns still apply

Quick Reference

Task	Code
Create client	TelegramClient(StringSession(session_str), api_id, api_hash)
Connect	await client.connect()
Get entity	entity = await client.get_entity(identifier)
Normalize ID	from telethon.utils import get_peer_id; get_peer_id(entity)
Iterate messages	async for msg in client.iter_messages(chat, limit=100):
Join by invite	await client(ImportChatInviteRequest(hash_val))
Handle flood	except FloodWaitError as e: await asyncio.sleep(e.seconds)
Save session	session_string = client.session.save()

Critical Gotchas

Gotcha	What Breaks	Fix
Boolean fields are None not False	NOT NULL DB columns	getattr(obj, field, False) or False
isinstance() fails with test mocks	Media/reaction type detection	type(obj).__name__ string comparison
iter_messages() has no max_date	Date filtering silently skipped	Filter post-fetch: if msg.date > max_date: continue
to_dict() returns bytes in polls	JSONB serialization crashes	Base64-encode bytes before storage
New types missing in older versions	ImportError at startup	Guard with try/except ImportError
ReactionCount.chosen removed in 1.42	AttributeError	getattr(r, 'chosen_order', None) is not None
get_peer_id() on non-standard objects	TypeError	try/except, fallback getattr(entity, 'id', 0)
MessageDeleted non-channel events	chat_id is None	Always guard if event.chat_id is not None
Stop listener before pool	Dangling handler errors	listener.stop() then pool.stop()
aggressive=True on iter_participants	Triggers flood waits faster	Use ChannelParticipantsSearch("") with pagination
2FA detection is string-based	Missed 2FA prompts	Catch SessionPasswordNeededError explicitly

Session Management

Always use StringSession — never file sessions. Store in env vars; treat as passwords (full account access).

from telethon import TelegramClient
from telethon.sessions import StringSession

client = TelegramClient(StringSession(os.getenv("TG_SESSION")), api_id, api_hash)
await client.connect()
if not await client.is_user_authorized():
    await client.send_code_request(phone)
    await client.sign_in(phone, code)
session_string = client.session.save()  # Save to env var after auth

FloodWaitError Handling

The raw pattern (basis for all wrappers):

except FloodWaitError as e:
    await asyncio.sleep(e.seconds)  # e.seconds = mandatory wait duration
    # then retry or rotate to next account

Three wrapper patterns — see telethon-reference.md for implementations:

Pattern	When to Use
Decorator	Single async calls (get_entity, get_messages)
Iterator wrapper	async for loops — supports checkpoint resume on retry
Context manager	Complex control flow, manual checkpoint tracking

Type Detection (Mock-Safe)

Use class name strings — works with both real Telethon objects AND test mocks:

attr_name = type(attr).__name__
if attr_name == "DocumentAttributeVideo":
    return "video_note" if getattr(attr, "round_message", False) else "video"

if type(reaction).__name__ == "ReactionEmoji":
    return reaction.emoticon

Version Guards

Always guard imports for types added in recent Telethon versions:

try:
    from telethon.tl.types import MessageMediaPaidMedia
except ImportError:
    MessageMediaPaidMedia = None

Entity Resolution & ID Normalization

from telethon.utils import get_peer_id

entity = await client.get_entity(identifier)  # str, int, or @username
normalized_id = get_peer_id(entity)            # Canonical ID for DB storage

See telethon-reference.md for channel type detection and all link format parsing.

Rate Limiting Guidelines

Operation	Safe Rate	Risk
Messages in single chat	1/second	Flood ban
Channel joins	2-5s between	Account freeze
Participant scraping (no takeout)	Don't	Instant ban
Channels scraped per day	<200	24h soft ban
Mass avatar downloads	Don't	Ban after 3-5

Use takeout sessions for heavy participant scraping — see telethon-reference.md.

Common Errors

Error	Meaning	Handle
FloodWaitError	Rate limited	Wait e.seconds, rotate account
AuthKeyUnregisteredError	Session invalid	Disable account permanently
ChannelPrivateError	No access	Skip, log
ChatAdminRequiredError	Need admin	Return empty, log
UserAlreadyParticipantError	Already joined	Not an error — treat as success
InviteRequestSentError	Needs approval	Log as pending
PhoneNumberBannedError	Account banned	Disable permanently

Test Mocking

See telethon-reference.md for complete patterns:

• Mock client fixture with async generators
• RPC call mocking (client(Request()))
• spec= for isinstance() compatibility
• FloodWaitError construction: FloodWaitError(request=None, capture=0.01)