# public chat
from telethon.tl.functions.channels import JoinChannelRequest
await client(JoinChannelRequest(channel))
# private chat
from telethon.tl.functions.messages import ImportChatInviteRequest
updates = await client(ImportChatInviteRequest('AAAAAEHbEkejzxUjAUCfYg'))
Here is what the above code is Doing:
1. Importing the required functions from the telethon.tl.functions module.
2. Calling the function with the client.
3. Awaiting the result.
The result is an Updates object, which is a list of updates.