Updates in Depth¶
Properties vs. Methods¶
The event shown above acts just like a custom.Message
, which means you
can access all the properties it has, like .sender
.
However events are different to other methods in the client, like
client.get_messages
.
Events may not send information about the sender or chat, which means it
can be None
, but all the methods defined in the client always have this
information so it doesn’t need to be re-fetched. For this reason, you have
get_
methods, which will make a network call if necessary.
In short, you should do this:
@client.on(events.NewMessage)
async def handler(event):
# event.input_chat may be None, use event.get_input_chat()
chat = await event.get_input_chat()
sender = await event.get_sender()
buttons = await event.get_buttons()
async def main():
async for message in client.iter_messages('me', 10):
# Methods from the client always have these properties ready
chat = message.input_chat
sender = message.sender
buttons = message.buttons
Notice, properties (message.sender
) don’t need an await
, but
methods (message.get_sender
) do need an await
,
and you should use methods in events for these properties that may need network.
Events Without the client¶
The code of your application starts getting big, so you decide to
separate the handlers into different files. But how can you access
the client from these files? You don’t need to! Just events.register
them:
# handlers/welcome.py
from telethon import events
@events.register(events.NewMessage('(?i)hello'))
async def handler(event):
client = event.client
await event.respond('Hey!')
await client.send_message('me', 'I said hello to someone')
Registering events is a way of saying “this method is an event handler”.
You can use telethon.events.is_handler
to check if any method is a handler.
You can think of them as a different approach to Flask’s blueprints.
It’s important to note that this does not add the handler to any client! You never specified the client on which the handler should be used. You only declared that it is a handler, and its type.
To actually use the handler, you need to client.add_event_handler
to the
client (or clients) where they should be added to:
# main.py
from telethon import TelegramClient
import handlers.welcome
with TelegramClient(...) as client:
client.add_event_handler(handlers.welcome.handler)
client.run_until_disconnected()
This also means that you can register an event handler once and then add it to many clients without re-declaring the event.
Events Without Decorators¶
If for any reason you don’t want to use telethon.events.register
,
you can explicitly pass the event handler to use to the mentioned
client.add_event_handler
:
from telethon import TelegramClient, events
async def handler(event):
...
with TelegramClient(...) as client:
client.add_event_handler(handler, events.NewMessage)
client.run_until_disconnected()
Similarly, you also have client.remove_event_handler
and client.list_event_handlers
.
The event
argument is optional in all three methods and defaults to
events.Raw
for adding, and None
when
removing (so all callbacks would be removed).
Note
The event
type is ignored in client.add_event_handler
if you have used telethon.events.register
on the callback
before, since that’s the point of using such method at all.
Stopping Propagation of Updates¶
There might be cases when an event handler is supposed to be used solitary and
it makes no sense to process any other handlers in the chain. For this case,
it is possible to raise a telethon.events.StopPropagation
exception which
will cause the propagation of the update through your handlers to stop:
from telethon.events import StopPropagation
@client.on(events.NewMessage)
async def _(event):
# ... some conditions
await event.delete()
# Other handlers won't have an event to work with
raise StopPropagation
@client.on(events.NewMessage)
async def _(event):
# Will never be reached, because it is the second handler
# in the chain.
pass
Remember to check Update Events if you’re looking for the methods reference.
Understanding asyncio¶
With asyncio
, the library has several tasks running in the background.
One task is used for sending requests, another task is used to receive them,
and a third one is used to handle updates.
To handle updates, you must keep your script running. You can do this in
several ways. For instance, if you are not running asyncio
’s event
loop, you should use client.run_until_disconnected
:
import asyncio
from telethon import TelegramClient
client = TelegramClient(...)
...
client.run_until_disconnected()
Behind the scenes, this method is await
’ing on the client.disconnected
property,
so the code above and the following are equivalent:
import asyncio
from telethon import TelegramClient
client = TelegramClient(...)
async def main():
await client.disconnected
asyncio.run(main())
You could also run client.disconnected
until it completed.
But if you don’t want to await
, then you should know what you want
to be doing instead! What matters is that you shouldn’t let your script
die. If you don’t care about updates, you don’t need any of this.
Notice that unlike client.disconnected
,
client.run_until_disconnected
will
handle KeyboardInterrupt
for you. This method is special and can
also be ran while the loop is running, so you can do this:
async def main():
await client.run_until_disconnected()
loop.run_until_complete(main())
Sequential Updates¶
If you need to process updates sequentially (i.e. not in parallel),
you should set sequential_updates=True
when creating the client:
with TelegramClient(..., sequential_updates=True) as client:
...