Change stderr prints to use the logging module instead

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>`