Add a new docs page for Chats vs Channels

readthedocs/concepts/chats-vs-channels.rst

@@ -0,0 +1,169 @@
+.. _chats-channels:
+
+=================
+Chats vs Channels
+=================
+
+Telegram's raw API can get very confusing sometimes, in particular when it
+comes to talking about "chats", "channels", "groups", "megagroups", and all
+those concepts.
+
+This section will try to explain what each of these concepts are.
+
+
+Chats
+=====
+
+A ``Chat`` can be used to talk about either the common "subclass" that both
+chats and channels share, or the concrete :tl:`Chat` type.
+
+Technically, both :tl:`Chat` and :tl:`Channel` are a form of the `Chat type`_.
+
+**Most of the time**, the term :tl:`Chat` is used to talk about *small group
+chats*. When you create a group through an official application, this is the
+type that you get. Official applications refer to these as "Group".
+
+Both the bot API and Telethon will add a minus sign (negate) the real chat ID
+so that you can tell at a glance, with just a number, the entity type.
+
+For example, if you create a chat with :tl:`CreateChatRequest`, the real chat
+ID might be something like `123`. If you try printing it from a
+`message.chat_id` you will see `-123`. This ID helps Telethon know you're
+talking about a :tl:`Chat`.
+
+
+Channels
+========
+
+Official applications create a *broadcast* channel when you create a new
+channel (used to broadcast messages, only administrators can post messages).
+
+Official applications implicitly *migrate* an *existing* :tl:`Chat` to a
+*megagroup* :tl:`Channel` when you perform certain actions (exceed user limit,
+add a public username, set certain permissions, etc.).
+
+A ``Channel`` can be created directly with :tl:`CreateChannelRequest`, as
+either a ``megagroup`` or ``broadcast``.
+
+Official applications use the term "channel" **only** for broadcast channels.
+
+The API refers to the different types of :tl:`Channel` with certain attributes:
+
+* A **broadcast channel** is a :tl:`Channel` with the ``channel.broadcast``
+  attribute set to `True`.
+
+* A **megagroup channel** is a :tl:`Channel` with the ``channel.megagroup``
+  attribute set to `True`. Official applications refer to this as "supergroup".
+
+* A **gigagroup channel** is a :tl:`Channel` with the ``channel.gigagroup``
+  attribute set to `True`. Official applications refer to this as "broadcast
+  groups", and is used when a megagroup becomes very large and administrators
+  want to transform it into something where only they can post messages.
+
+
+Both the bot API and Telethon will "concatenate" ``-100`` to the real chat ID
+so that you can tell at a glance, with just a number, the entity type.
+
+For example, if you create a new broadcast channel, the real channel ID might
+be something like `456`. If you try printing it from a `message.chat_id` you
+will see `-1000000000456`. This ID helps Telethon know you're talking about a
+:tl:`Channel`.
+
+
+Converting IDs
+==============
+
+You can convert between the "marked" identifiers (prefixed with a minus sign)
+and the real ones with ``utils.resolve_id``. It will return a tuple with the
+real ID, and the peer type (the class):
+
+.. code-block:: python
+
+    from telethon import utils
+    real_id, peer_type = utils.resolve_id(-1000000000456)
+
+    print(real_id)  # 456
+    print(peer_type)  # <class 'telethon.tl.types.PeerChannel'>
+
+    peer = peer_type(real_id)
+    print(peer)  # PeerChannel(channel_id=456)
+
+
+The reverse operation can be done with ``utils.get_peer_id``:
+
+.. code-block:: python
+
+    print(utils.get_peer_id(types.PeerChannel(456)))  # -1000000000456
+
+
+Note that this function can also work with other types, like :tl:`Chat` or
+:tl:`Channel` instances.
+
+If you need to convert other types like usernames which might need to perform
+API calls to find out the identifier, you can use ``client.get_peer_id``:
+
+
+.. code-block:: python
+
+    print(await client.get_peer_id('me'))  # your id
+
+
+If there is no "mark" (no minus sign), Telethon will assume your identifier
+refers to a :tl:`User`. If this is **not** the case, you can manually fix it:
+
+
+.. code-block:: python
+
+    from telethon import types
+    await client.send_message(types.PeerChannel(456), 'hello')
+    #                         ^^^^^^^^^^^^^^^^^ explicit peer type
+
+
+A note on raw API
+=================
+
+Certain methods only work on a :tl:`Chat`, and some others only work on a
+:tl:`Channel` (and these may only work in broadcast, or megagroup). Your code
+likely knows what it's working with, so it shouldn't be too much of an issue.
+
+If you need to find the :tl:`Channel` from a :tl:`Chat` that migrated to it,
+access the `migrated_to` property:
+
+.. code-block:: python
+
+    # chat is a Chat
+    channel = await client.get_entity(chat.migrated_to)
+    # channel is now a Channel
+
+Channels do not have a "migrated_from", but a :tl:`ChannelFull` does. You can
+use :tl:`GetFullChannelRequest` to obtain this:
+
+.. code-block:: python
+
+    from telethon import functions
+    full = await client(functions.channels.GetFullChannelRequest(your_channel))
+    full_channel = full.full_chat
+    # full_channel is a ChannelFull
+    print(full_channel.migrated_from_chat_id)
+
+This way, you can also access the linked discussion megagroup of a broadcast channel:
+
+.. code-block:: python
+
+    print(full_channel.linked_chat_id)  # prints ID of linked discussion group or None
+
+You do not need to use ``client.get_entity`` to access the
+``migrated_from_chat_id`` :tl:`Chat` or the ``linked_chat_id`` :tl:`Channel`.
+They are in the ``full.chats`` attribute:
+
+.. code-block:: python
+
+    if full_channel.migrated_from_chat_id:
+        migrated_from_chat = next(c for c in full.chats if c.id == full_channel.migrated_from_chat_id)
+        print(migrated_from_chat.title)
+
+    if full_channel.linked_chat_id:
+        linked_group = next(c for c in full.chats if c.id == full_channel.linked_chat_id)
+        print(linked_group.username)
+
+.. _Chat type: https://tl.telethon.dev/types/chat.html

readthedocs/index.rst

@@ -68,6 +68,7 @@ You can also use the menu on the left to quickly skip over sections.
 
     concepts/strings
     concepts/entities
+    concepts/chats-vs-channels
     concepts/updates
     concepts/sessions
     concepts/full-api