Change stderr prints to use the logging module instead

discord/app_commands/tree.py

@@ -23,9 +23,8 @@ DEALINGS IN THE SOFTWARE.
 """
 
 from __future__ import annotations
+import logging
 import inspect
-import sys
-import traceback
 
 from typing import (
     Any,
@@ -79,6 +78,8 @@ __all__ = ('CommandTree',)
 
 ClientT = TypeVar('ClientT', bound='Client')
 
+_log = logging.getLogger(__name__)
+
 
 def _retrieve_guild_ids(
     command: Any, guild: Optional[Snowflake] = MISSING, guilds: Sequence[Snowflake] = MISSING
@@ -775,8 +776,8 @@ class CommandTree(Generic[ClientT]):
 
         A callback that is called when any command raises an :exc:`AppCommandError`.
 
-        The default implementation prints the traceback to stderr if the command does
-        not have any error handlers attached to it.
+        The default implementation logs the exception using the library logger
+        if the command does not have any error handlers attached to it.
 
         To get the command that failed, :attr:`discord.Interaction.command` should
         be used.
@@ -794,11 +795,9 @@ class CommandTree(Generic[ClientT]):
             if command._has_any_error_handlers():
                 return
 
-            print(f'Ignoring exception in command {command.name!r}:', file=sys.stderr)
+            _log.error('Ignoring exception in command %r', command.name, exc_info=error)
         else:
-            print(f'Ignoring exception in command tree:', file=sys.stderr)
-
-        traceback.print_exception(error.__class__, error, error.__traceback__, file=sys.stderr)
+            _log.error('Ignoring exception in command tree', exc_info=error)
 
     def error(self, coro: ErrorFunc) -> ErrorFunc:
         """A decorator that registers a coroutine as a local error handler.

discord/client.py

@@ -29,7 +29,6 @@ import datetime
 import logging
 import sys
 import os
-import traceback
 from typing import (
     Any,
     AsyncIterator,
@@ -519,16 +518,16 @@ class Client:
 
         The default error handler provided by the client.
 
-        By default this prints to :data:`sys.stderr` however it could be
+        By default this logs to the library logger however it could be
         overridden to have a different implementation.
         Check :func:`~discord.on_error` for more details.
 
         .. versionchanged:: 2.0
 
-            ``event_method`` parameter is now positional-only.
+            ``event_method`` parameter is now positional-only
+            and instead of writing to ``sys.stderr`` it logs instead.
         """
-        print(f'Ignoring exception in {event_method}', file=sys.stderr)
-        traceback.print_exc()
+        _log.exception('Ignoring exception in %s', event_method)
 
     # hooks
 

discord/ext/commands/bot.py

@@ -31,7 +31,7 @@ import collections.abc
 import inspect
 import importlib.util
 import sys
-import traceback
+import logging
 import types
 from typing import (
     Any,
@@ -95,6 +95,8 @@ __all__ = (
 T = TypeVar('T')
 CFT = TypeVar('CFT', bound='CoroFunc')
 
+_log = logging.getLogger(__name__)
+
 
 def when_mentioned(bot: _Bot, msg: Message, /) -> List[str]:
     """A callable that implements a command prefix equivalent to being mentioned.
@@ -304,7 +306,7 @@ class BotBase(GroupMixin[None]):
 
         The default command error handler provided by the bot.
 
-        By default this prints to :data:`sys.stderr` however it could be
+        By default this logs to the library logger, however it could be
         overridden to have a different implementation.
 
         This only fires if you do not specify any listeners for command error.
@@ -312,6 +314,7 @@ class BotBase(GroupMixin[None]):
         .. versionchanged:: 2.0
 
             ``context`` and ``exception`` parameters are now positional-only.
+            Instead of writing to ``sys.stderr`` this now uses the library logger.
         """
         if self.extra_events.get('on_command_error', None):
             return
@@ -324,8 +327,7 @@ class BotBase(GroupMixin[None]):
         if cog and cog.has_error_handler():
             return
 
-        print(f'Ignoring exception in command {context.command}:', file=sys.stderr)
-        traceback.print_exception(type(exception), exception, exception.__traceback__, file=sys.stderr)
+        _log.error('Ignoring exception in command %s', command, exc_info=exception)
 
     # global check registration
 

discord/ext/tasks/__init__.py

@@ -42,8 +42,6 @@ from typing import (
 import aiohttp
 import discord
 import inspect
-import sys
-import traceback
 
 from collections.abc import Sequence
 from discord.backoff import ExponentialBackoff
@@ -536,8 +534,7 @@ class Loop(Generic[LF]):
 
     async def _error(self, *args: Any) -> None:
         exception: Exception = args[-1]
-        print(f'Unhandled exception in internal background task {self.coro.__name__!r}.', file=sys.stderr)
-        traceback.print_exception(type(exception), exception, exception.__traceback__, file=sys.stderr)
+        _log.error('Unhandled exception in internal background task %r.', self.coro.__name__, exc_info=exception)
 
     def before_loop(self, coro: FT) -> FT:
         """A decorator that registers a coroutine to be called before the loop starts running.
@@ -600,11 +597,15 @@ class Loop(Generic[LF]):
 
         The coroutine must take only one argument the exception raised (except ``self`` in a class context).
 
-        By default this prints to :data:`sys.stderr` however it could be
+        By default this logs to the library logger however it could be
         overridden to have a different implementation.
 
         .. versionadded:: 1.4
 
+        .. versionchanged:: 2.0
+
+            Instead of writing to ``sys.stderr``, the library's logger is used.
+
         Parameters
         ------------
         coro: :ref:`coroutine <coroutine>`