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/activity.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 """
 The MIT License (MIT)
 
@@ -196,16 +194,16 @@ class Activity(BaseActivity):
 
     def __repr__(self):
         attrs = (
-            'type',
-            'name',
-            'url',
-            'details',
-            'application_id',
-            'session_id',
-            'emoji',
+            ('type', self.type),
+            ('name', self.name),
+            ('url', self.url),
+            ('details', self.details),
+            ('application_id', self.application_id),
+            ('session_id', self.session_id),
+            ('emoji', self.emoji),
         )
-        mapped = ' '.join('%s=%r' % (attr, getattr(self, attr)) for attr in attrs)
-        return '<Activity %s>' % mapped
+        inner = ' '.join('%s=%r' % t for t in attrs)
+        return f'<Activity {inner}>'
 
     def to_dict(self):
         ret = {}
@@ -250,7 +248,7 @@ class Activity(BaseActivity):
         except KeyError:
             return None
         else:
-            return Asset.BASE + '/app-assets/{0}/{1}.png'.format(self.application_id, large_image)
+            return Asset.BASE + f'/app-assets/{self.application_id}/{large_image}.png'
 
     @property
     def small_image_url(self):
@@ -263,7 +261,7 @@ class Activity(BaseActivity):
         except KeyError:
             return None
         else:
-            return Asset.BASE + '/app-assets/{0}/{1}.png'.format(self.application_id, small_image)
+            return Asset.BASE + f'/app-assets/{self.application_id}/{small_image}.png'
     @property
     def large_image_text(self):
         """Optional[:class:`str`]: Returns the large image asset hover text of this activity if applicable."""
@@ -362,7 +360,7 @@ class Game(BaseActivity):
         return str(self.name)
 
     def __repr__(self):
-        return '<Game name={0.name!r}>'.format(self)
+        return f'<Game name={self.name!r}>'
 
     def to_dict(self):
         timestamps = {}
@@ -455,7 +453,7 @@ class Streaming(BaseActivity):
         return str(self.name)
 
     def __repr__(self):
-        return '<Streaming name={0.name!r}>'.format(self)
+        return f'<Streaming name={self.name!r}>'
 
     @property
     def twitch_name(self):
@@ -700,7 +698,7 @@ class CustomActivity(BaseActivity):
         elif isinstance(emoji, PartialEmoji):
             self.emoji = emoji
         else:
-            raise TypeError('Expected str, PartialEmoji, or None, received {0!r} instead.'.format(type(emoji)))
+            raise TypeError(f'Expected str, PartialEmoji, or None, received {type(emoji)!r} instead.')
 
     @property
     def type(self):
@@ -739,7 +737,7 @@ class CustomActivity(BaseActivity):
     def __str__(self):
         if self.emoji:
             if self.name:
-                return '%s %s' % (self.emoji, self.name)
+                return f'{self.emoji} {self.name}'
             return str(self.emoji)
         else:
             return str(self.name)