feat: add once decorator to discord.Client (#1940)

Signed-off-by: Om <92863779+Om1609@users.noreply.github.com>
Co-authored-by: BobDotCom <71356958+BobDotCom@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -15,6 +15,8 @@ These changes are available on the `master` branch, but have not yet been releas
 - Added new events `on_bridge_command`, `on_bridge_command_completion`, and
   `on_bridge_command_error`.
   ([#1916](https://github.com/Pycord-Development/pycord/pull/1916))
+- Added the `@client.once()` decorator, which serves as a one-time event listener.
+  ([#1940](https://github.com/Pycord-Development/pycord/pull/1940))
 
 ### Fixed
 

discord/client.py

@@ -1286,6 +1286,64 @@ async def on_ready():
         _log.debug("%s has successfully been registered as an event", coro.__name__)
         return coro
 
+    def once(
+        self, name: str = MISSING, check: Callable[..., bool] | None = None
+    ) -> Coro:
+        """A decorator that registers an event to listen to only once.
+
+        You can find more info about the events on the :ref:`documentation below <discord-api-events>`.
+
+        The events must be a :ref:`coroutine <coroutine>`, if not, :exc:`TypeError` is raised.
+
+        Parameters
+        ----------
+        name: :class:`str`
+            The name of the event we want to listen to. This is passed to
+            :py:meth:`~discord.Client.wait_for`. Defaults to ``func.__name__``.
+        check: Optional[Callable[..., :class:`bool`]]
+            A predicate to check what to wait for. The arguments must meet the
+            parameters of the event being waited for.
+
+        Raises
+        ------
+        TypeError
+            The coroutine passed is not actually a coroutine.
+
+        Example
+        -------
+
+        .. code-block:: python3
+
+            @client.once()
+            async def ready():
+                print('Ready!')
+        """
+
+        def decorator(func: Coro) -> Coro:
+            if not asyncio.iscoroutinefunction(func):
+                raise TypeError("event registered must be a coroutine function")
+
+            async def wrapped() -> None:
+                nonlocal name
+                nonlocal check
+
+                name = func.__name__ if name is MISSING else name
+
+                args = await self.wait_for(name, check=check)
+
+                arg_len = func.__code__.co_argcount
+                if arg_len == 0 and args is None:
+                    await func()
+                elif arg_len == 1:
+                    await func(args)
+                else:
+                    await func(*args)
+
+            self.loop.create_task(wrapped())
+            return func
+
+        return decorator
+
     async def change_presence(
         self,
         *,

docs/api/clients.rst

@@ -10,7 +10,7 @@ Bots
 .. autoclass:: Bot
     :members:
     :inherited-members:
-    :exclude-members: command, event, message_command, slash_command, user_command, listen
+    :exclude-members: command, event, message_command, slash_command, user_command, listen, once
 
     .. automethod:: Bot.command(**kwargs)
         :decorator:
@@ -30,6 +30,9 @@ Bots
     .. automethod:: Bot.listen(name=None)
         :decorator:
 
+    .. automethod:: Bot.once(name=None, check=None)
+        :decorator:
+
 .. attributetable:: AutoShardedBot
 .. autoclass:: AutoShardedBot
     :members:
@@ -41,14 +44,17 @@ Clients
 .. attributetable:: Client
 .. autoclass:: Client
     :members:
-    :exclude-members: fetch_guilds, event
+    :exclude-members: fetch_guilds, event, once
 
     .. automethod:: Client.event()
         :decorator:
 
     .. automethod:: Client.fetch_guilds
         :async-for:
 
+    .. automethod:: Client.once(name=None, check=None)
+        :decorator:
+
 .. attributetable:: AutoShardedClient
 .. autoclass:: AutoShardedClient
     :members:

docs/api/events.rst

@@ -7,10 +7,11 @@ Event Reference
 
 This section outlines the different types of events listened by :class:`Client`.
 
-There are 3 ways to register an event, the first way is through the use of
+There are 4 ways to register an event, the first way is through the use of
 :meth:`Client.event`. The second way is through subclassing :class:`Client` and
-overriding the specific events. The third way is through the use of :meth:`Client.listen`, which can be used to assign multiple
-event handlers instead of only one like in :meth:`Client.event`. For example:
+overriding the specific events. The third way is through the use of :meth:`Client.listen`,
+which can be used to assign multiple event handlers instead of only one like in :meth:`Client.event`.
+The fourth way is through the use of :meth:`Client.once`, which serves as a one-time event listener. For example:
 
 .. code-block:: python
     :emphasize-lines: 17, 22
@@ -40,6 +41,11 @@ event handlers instead of only one like in :meth:`Client.event`. For example:
     async def on_message(message: discord.Message):
         print(f"Received {message.content}")
 
+    # Runs only for the 1st 'on_message' event. Can be useful for listening to 'on_ready'
+    @client.once()
+    async def message(message: discord.Message):
+        print(f"Received {message.content}")
+
 
 If an event handler raises an exception, :func:`on_error` will be called
 to handle it, which defaults to print a traceback and ignoring the exception.

docs/ext/commands/api.rst

@@ -23,7 +23,7 @@ Bot
 .. autoclass:: discord.ext.commands.Bot
     :members:
     :inherited-members:
-    :exclude-members: after_invoke, before_invoke, check, check_once, command, event, group, listen
+    :exclude-members: after_invoke, before_invoke, check, check_once, command, event, group, listen, once
 
     .. automethod:: Bot.after_invoke()
         :decorator:
@@ -49,6 +49,9 @@ Bot
     .. automethod:: Bot.listen(name=None)
         :decorator:
 
+    .. automethod:: Bot.once(name=None, check=None)
+        :decorator:
+
 AutoShardedBot
 ~~~~~~~~~~~~~~