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/webhook.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 """
 The MIT License (MIT)
 
@@ -65,7 +63,7 @@ class WebhookAdapter:
     def _prepare(self, webhook):
         self._webhook_id = webhook.id
         self._webhook_token = webhook.token
-        self._request_url = '{0.BASE}/webhooks/{1}/{2}'.format(self, webhook.id, webhook.token)
+        self._request_url = f'{self.BASE}/webhooks/{webhook.id}/{webhook.token}'
         self.webhook = webhook
 
     def is_async(self):
@@ -100,10 +98,10 @@ class WebhookAdapter:
         return self.request('PATCH', self._request_url, payload=payload, reason=reason)
 
     def edit_webhook_message(self, message_id, payload):
-        return self.request('PATCH', '{}/messages/{}'.format(self._request_url, message_id), payload=payload)
+        return self.request('PATCH', f'{self._request_url}/messages/{message_id}', payload=payload)
 
     def delete_webhook_message(self, message_id):
-        return self.request('DELETE', '{}/messages/{}'.format(self._request_url, message_id))
+        return self.request('DELETE', f'{self._request_url}/messages/{message_id}')
 
     def handle_execution_response(self, data, *, wait):
         """Transforms the webhook execution response into something
@@ -158,7 +156,7 @@ class WebhookAdapter:
             multipart = None
             files_to_pass = None
 
-        url = '%s?wait=%d' % (self._request_url, wait)
+        url = f'{self._request_url}?wait={int(wait)}'
         maybe_coro = None
         try:
             maybe_coro = self.request('POST', url, multipart=multipart, payload=data, files=files_to_pass)
@@ -422,7 +420,7 @@ class _PartialWebhookState:
         if self.parent is not None:
             return getattr(self.parent, attr)
 
-        raise AttributeError('PartialWebhookState does not support {0!r}.'.format(attr))
+        raise AttributeError(f'PartialWebhookState does not support {attr!r}.')
 
 class WebhookMessage(Message):
     """Represents a message sent from your webhook.
@@ -623,12 +621,12 @@ class Webhook(Hashable):
             self.user = User(state=state, data=user)
 
     def __repr__(self):
-        return '<Webhook id=%r>' % self.id
+        return f'<Webhook id={self.id!r}>'
 
     @property
     def url(self):
         """:class:`str` : Returns the webhook's url."""
-        return 'https://discord.com/api/webhooks/{}/{}'.format(self.id, self.token)
+        return f'https://discord.com/api/webhooks/{self.id}/{self.token}'
 
     @classmethod
     def partial(cls, id, token, *, adapter):
@@ -697,7 +695,7 @@ class Webhook(Hashable):
 
     @classmethod
     def _as_follower(cls, data, *, channel, user):
-        name = "{} #{}".format(channel.guild, channel)
+        name = f"{channel.guild} #{channel}"
         feed = {
             'id': data['webhook_id'],
             'type': 2,