[commands] Add predicate attribute to checks to get inner function

discord/ext/commands/core.py

@@ -1307,10 +1307,27 @@ def check(predicate):
     will be propagated while those subclassed will be sent to
     :func:`.on_command_error`.
 
+    A special attribute named ``predicate`` is bound to the value
+    returned by this decorator to retrieve the predicate passed to the
+    decorator. This allows the following introspection and chaining to be done:
+
+    .. code-block:: python3
+
+        def owner_or_permissions(**perms):
+            original = commands.has_permissions(**perms).predicate
+            def extended_check(ctx):
+                if ctx.guild is None:
+                    return False
+                return ctx.guild.owner_id == ctx.author.id or original(ctx)
+            return commands.check(extended_check)
+
     .. note::
 
         These functions can either be regular functions or coroutines.
 
+    .. versionchanged:: 1.3.0
+        The ``predicate`` attribute was added.
+
     Examples
     ---------
 
@@ -1356,6 +1373,8 @@ def check(predicate):
             func.__commands_checks__.append(predicate)
 
         return func
+
+    decorator.predicate = predicate
     return decorator
 
 def has_role(item):
@@ -1374,6 +1393,10 @@ def has_role(item):
     is missing a role, or :exc:`.NoPrivateMessage` if it is used in a private message.
     Both inherit from :exc:`.CheckFailure`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionchanged:: 1.1.0
 
         Raise :exc:`.MissingRole` or :exc:`.NoPrivateMessage`
@@ -1410,6 +1433,10 @@ def has_any_role(*items):
     is missing all roles, or :exc:`.NoPrivateMessage` if it is used in a private message.
     Both inherit from :exc:`.CheckFailure`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionchanged:: 1.1.0
 
         Raise :exc:`.MissingAnyRole` or :exc:`.NoPrivateMessage`
@@ -1449,6 +1476,10 @@ def bot_has_role(item):
     is missing the role, or :exc:`.NoPrivateMessage` if it is used in a private message.
     Both inherit from :exc:`.CheckFailure`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionchanged:: 1.1.0
 
         Raise :exc:`.BotMissingRole` or :exc:`.NoPrivateMessage`
@@ -1478,6 +1509,10 @@ def bot_has_any_role(*items):
     is missing all roles, or :exc:`.NoPrivateMessage` if it is used in a private message.
     Both inherit from :exc:`.CheckFailure`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionchanged:: 1.1.0
 
         Raise :exc:`.BotMissingAnyRole` or :exc:`.NoPrivateMessage`
@@ -1508,6 +1543,10 @@ def has_permissions(**perms):
     This check raises a special exception, :exc:`.MissingPermissions`
     that is inherited from :exc:`.CheckFailure`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     Parameters
     ------------
     perms
@@ -1543,6 +1582,10 @@ def bot_has_permissions(**perms):
 
     This check raises a special exception, :exc:`.BotMissingPermissions`
     that is inherited from :exc:`.CheckFailure`.
+
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
     """
     def predicate(ctx):
         guild = ctx.guild
@@ -1565,6 +1608,10 @@ def has_guild_permissions(**perms):
     If this check is called in a DM context, it will raise an
     exception, :exc:`.NoPrivateMessage`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionadded:: 1.3.0
     """
     def predicate(ctx):
@@ -1585,6 +1632,10 @@ def bot_has_guild_permissions(**perms):
     """Similar to :func:`.has_guild_permissions`, but checks the bot
     members guild permissions.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionadded:: 1.3.0
     """
     def predicate(ctx):
@@ -1609,6 +1660,10 @@ def dm_only():
     This check raises a special exception, :exc:`.PrivateMessageOnly`
     that is inherited from :exc:`.CheckFailure`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionadded:: 1.1.0
     """
 
@@ -1626,6 +1681,10 @@ def guild_only():
 
     This check raises a special exception, :exc:`.NoPrivateMessage`
     that is inherited from :exc:`.CheckFailure`.
+
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
     """
 
     def predicate(ctx):
@@ -1643,6 +1702,10 @@ def is_owner():
 
     This check raises a special exception, :exc:`.NotOwner` that is derived
     from :exc:`.CheckFailure`.
+
+    .. note::
+
+        The ``predicate`` attribute for this function **is** a coroutine.
     """
 
     async def predicate(ctx):
@@ -1658,6 +1721,10 @@ def is_nsfw():
     This check raises a special exception, :exc:`.NSFWChannelRequired`
     that is derived from :exc:`.CheckFailure`.
 
+    .. note::
+
+        The ``predicate`` attribute for this function is **not** a coroutine.
+
     .. versionchanged:: 1.1.0
 
         Raise :exc:`.NSFWChannelRequired` instead of generic :exc:`.CheckFailure`.