Modernize code to use f-strings

This also removes the encoding on the top, since Python 3 does it by
default. It also changes some methods to use `yield from`.

discord/ext/commands/core.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 """
 The MIT License (MIT)
 
@@ -473,7 +471,7 @@ class Command(_BaseCommand):
             except AttributeError:
                 name = converter.__class__.__name__
 
-            raise BadArgument('Converting to "{}" failed for parameter "{}".'.format(name, param.name)) from exc
+            raise BadArgument(f'Converting to "{name}" failed for parameter "{param.name}".') from exc
 
     async def do_conversion(self, ctx, converter, argument, param):
         try:
@@ -775,7 +773,7 @@ class Command(_BaseCommand):
         ctx.command = self
 
         if not await self.can_run(ctx):
-            raise CheckFailure('The check functions for command {0.qualified_name} failed.'.format(self))
+            raise CheckFailure(f'The check functions for command {self.qualified_name} failed.')
 
         if self._max_concurrency is not None:
             await self._max_concurrency.acquire(ctx)
@@ -1014,23 +1012,23 @@ class Command(_BaseCommand):
                 # do [name] since [name=None] or [name=] are not exactly useful for the user.
                 should_print = param.default if isinstance(param.default, str) else param.default is not None
                 if should_print:
-                    result.append('[%s=%s]' % (name, param.default) if not greedy else
-                                  '[%s=%s]...' % (name, param.default))
+                    result.append(f'[{name}={param.default}]' if not greedy else
+                                  f'[{name}={param.default}]...')
                     continue
                 else:
-                    result.append('[%s]' % name)
+                    result.append(f'[{name}]')
 
             elif param.kind == param.VAR_POSITIONAL:
                 if self.require_var_positional:
-                    result.append('<%s...>' % name)
+                    result.append(f'<{name}...>')
                 else:
-                    result.append('[%s...]' % name)
+                    result.append(f'[{name}...]')
             elif greedy:
-                result.append('[%s]...' % name)
+                result.append(f'[{name}]...')
             elif self._is_typing_optional(param.annotation):
-                result.append('[%s]' % name)
+                result.append(f'[{name}]')
             else:
-                result.append('<%s>' % name)
+                result.append(f'<{name}>')
 
         return ' '.join(result)
 
@@ -1062,14 +1060,14 @@ class Command(_BaseCommand):
         """
 
         if not self.enabled:
-            raise DisabledCommand('{0.name} command is disabled'.format(self))
+            raise DisabledCommand(f'{self.name} command is disabled')
 
         original = ctx.command
         ctx.command = self
 
         try:
             if not await ctx.bot.can_run(ctx):
-                raise CheckFailure('The global check functions for command {0.qualified_name} failed.'.format(self))
+                raise CheckFailure(f'The global check functions for command {self.qualified_name} failed.')
 
             cog = self.cog
             if cog is not None:
@@ -1588,7 +1586,7 @@ def check_any(*checks):
         try:
             pred = wrapped.predicate
         except AttributeError:
-            raise TypeError('%r must be wrapped by commands.check decorator' % wrapped) from None
+            raise TypeError(f'{wrapped!r} must be wrapped by commands.check decorator') from None
         else:
             unwrapped.append(pred)
 
@@ -1776,7 +1774,7 @@ def has_permissions(**perms):
 
     invalid = set(perms) - set(discord.Permissions.VALID_FLAGS)
     if invalid:
-        raise TypeError('Invalid permission(s): %s' % (', '.join(invalid)))
+        raise TypeError(f"Invalid permission(s): {', '.join(invalid)}")
 
     def predicate(ctx):
         ch = ctx.channel
@@ -1801,7 +1799,7 @@ def bot_has_permissions(**perms):
 
     invalid = set(perms) - set(discord.Permissions.VALID_FLAGS)
     if invalid:
-        raise TypeError('Invalid permission(s): %s' % (', '.join(invalid)))
+        raise TypeError(f"Invalid permission(s): {', '.join(invalid)}")
 
     def predicate(ctx):
         guild = ctx.guild
@@ -1829,7 +1827,7 @@ def has_guild_permissions(**perms):
 
     invalid = set(perms) - set(discord.Permissions.VALID_FLAGS)
     if invalid:
-        raise TypeError('Invalid permission(s): %s' % (', '.join(invalid)))
+        raise TypeError(f"Invalid permission(s): {', '.join(invalid)}")
 
     def predicate(ctx):
         if not ctx.guild:
@@ -1854,7 +1852,7 @@ def bot_has_guild_permissions(**perms):
 
     invalid = set(perms) - set(discord.Permissions.VALID_FLAGS)
     if invalid:
-        raise TypeError('Invalid permission(s): %s' % (', '.join(invalid)))
+        raise TypeError(f"Invalid permission(s): {', '.join(invalid)}")
 
     def predicate(ctx):
         if not ctx.guild:
@@ -1961,7 +1959,7 @@ def cooldown(rate, per, type=BucketType.default):
         The amount of seconds to wait for a cooldown when it's been triggered.
     type: Union[:class:`.BucketType`, Callable[[:class:`.Message`], Any]]
         The type of cooldown to have. If callable, should return a key for the mapping.
-        
+
         .. versionchanged:: 1.7
             Callables are now supported for custom bucket types.
     """