Make discord.Embed builder more strict and easier to use.

Allow for easier use when trying to "reuse" the same discord.Embed
object by providing new methods such as Embed.clear_fields,
Embed.set_field_at, and allowing you to set things to Embed.Empty to
clear out an attribute.

For ease of use, things are automatically casted to ``str`` to prevent
the user from having HTTP 400 errors if they forgot to do so. The new
embed builder also supports "fluent-style" interface to allow you to
chain methods in a single line if necessary.

Certain parameters were removed since they were ignored by Discord
anyway such as `width` and `height` in Embed.set_image and
Embed.set_thumbnail.

discord/embeds.py

@@ -60,6 +60,9 @@ class Embed:
     is invalid or empty, then a special sentinel value is returned,
     :attr:`Embed.Empty`.
 
+    For ease of use, all parameters that expect a ``str`` are implicitly
+    casted to ``str`` for you.
+
     Attributes
     -----------
     title: str
@@ -75,8 +78,8 @@ class Embed:
     colour: :class:`Colour` or int
         The colour code of the embed. Aliased to ``color`` as well.
     Empty
-        A special sentinel value used by ``EmbedProxy`` to denote
+        A special sentinel value used by ``EmbedProxy`` and this class
-        that the value or attribute is empty.
+        to denote that the value or attribute is empty.
     """
 
     __slots__ = ('title', 'url', 'type', '_timestamp', '_colour', '_footer',
@@ -90,15 +93,13 @@ class Embed:
         try:
             colour = kwargs['colour']
         except KeyError:
-            colour = kwargs.get('color')
+            colour = kwargs.get('color', EmptyEmbed)
-
-        if colour is not None:
-            self.colour = colour
 
-        self.title = kwargs.get('title')
+        self.colour = colour
+        self.title = kwargs.get('title', EmptyEmbed)
         self.type = kwargs.get('type', 'rich')
-        self.url = kwargs.get('url')
+        self.url = kwargs.get('url', EmptyEmbed)
-        self.description = kwargs.get('description')
+        self.description = kwargs.get('description', EmptyEmbed)
 
         try:
             timestamp = kwargs['timestamp']
@@ -114,10 +115,10 @@ class Embed:
 
         # fill in the basic fields
 
-        self.title = data.get('title')
+        self.title = data.get('title', EmptyEmbed)
-        self.type  = data.get('type')
+        self.type  = data.get('type', EmptyEmbed)
-        self.description = data.get('description')
+        self.description = data.get('description', EmptyEmbed)
-        self.url = data.get('url')
+        self.url = data.get('url', EmptyEmbed)
 
         # try to fill in the more rich fields
 
@@ -143,29 +144,29 @@ class Embed:
 
     @property
     def colour(self):
-        return getattr(self, '_colour', None)
+        return getattr(self, '_colour', EmptyEmbed)
 
     @colour.setter
     def colour(self, value):
-        if isinstance(value, Colour):
+        if isinstance(value, (Colour, _EmptyEmbed)):
             self._colour = value
         elif isinstance(value, int):
             self._colour = Colour(value=value)
         else:
-            raise TypeError('Expected discord.Colour or int, received %s instead.' % value.__class__.__name__)
+            raise TypeError('Expected discord.Colour, int, or Embed.Empty but received %s instead.' % value.__class__.__name__)
 
     color = colour
 
     @property
     def timestamp(self):
-        return getattr(self, '_timestamp', None)
+        return getattr(self, '_timestamp', EmptyEmbed)
 
     @timestamp.setter
     def timestamp(self, value):
-        if isinstance(value, datetime.datetime):
+        if isinstance(value, (datetime.datetime, _EmptyEmbed)):
             self._timestamp = value
         else:
-            raise TypeError("Expected datetime.datetime received %s instead" % value.__class__.__name__)
+            raise TypeError("Expected datetime.datetime or Embed.Empty received %s instead" % value.__class__.__name__)
 
     @property
     def footer(self):
@@ -173,13 +174,16 @@ class Embed:
 
         See :meth:`set_footer` for possible values you can access.
 
-        If the attribute cannot be accessed then ``None`` is returned.
+        If the attribute has no value then :attr:`Empty` is returned.
         """
         return EmbedProxy(getattr(self, '_footer', {}))
 
-    def set_footer(self, *, text=None, icon_url=None):
+    def set_footer(self, *, text=EmptyEmbed, icon_url=EmptyEmbed):
         """Sets the footer for the embed content.
 
+        This function returns the class instance to allow for fluent-style
+        chaining.
+
         Parameters
         -----------
         text: str
@@ -189,77 +193,79 @@ class Embed:
         """
 
         self._footer = {}
-        if text is not None:
+        if text is not EmptyEmbed:
-            self._footer['text'] = text
+            self._footer['text'] = str(text)
 
-        if icon_url is not None:
+        if icon_url is not EmptyEmbed:
-            self._footer['icon_url'] = icon_url
+            self._footer['icon_url'] = str(icon_url)
+
+        return self
 
     @property
     def image(self):
         """Returns a ``EmbedProxy`` denoting the image contents.
 
-        See :meth:`set_image` for possible values you can access.
+        Possible attributes you can access are:
+
+        - ``url``
+        - ``proxy_url``
+        - ``width``
+        - ``height``
 
-        If the attribute cannot be accessed then ``None`` is returned.
+        If the attribute has no value then :attr:`Empty` is returned.
         """
         return EmbedProxy(getattr(self, '_image', {}))
 
-    def set_image(self, *, url, height=None, width=None):
+    def set_image(self, *, url):
         """Sets the image for the embed content.
 
+        This function returns the class instance to allow for fluent-style
+        chaining.
+
         Parameters
         -----------
         url: str
             The source URL for the image. Only HTTP(S) is supported.
-        height: int
-            The height of the image.
-        width: int
-            The width of the image.
         """
 
         self._image = {
-            'url': url
+            'url': str(url)
         }
 
-        if height is not None:
+        return self
-            self._image['height'] = height
-
-        if width is not None:
-            self._image['width'] = width
 
     @property
     def thumbnail(self):
         """Returns a ``EmbedProxy`` denoting the thumbnail contents.
 
-        See :meth:`set_thumbnail` for possible values you can access.
+        Possible attributes you can access are:
+
+        - ``url``
+        - ``proxy_url``
+        - ``width``
+        - ``height``
 
-        If the attribute cannot be accessed then ``None`` is returned.
+        If the attribute has no value then :attr:`Empty` is returned.
         """
         return EmbedProxy(getattr(self, '_thumbnail', {}))
 
-    def set_thumbnail(self, *, url, height=None, width=None):
+    def set_thumbnail(self, *, url):
         """Sets the thumbnail for the embed content.
 
+        This function returns the class instance to allow for fluent-style
+        chaining.
+
         Parameters
         -----------
         url: str
             The source URL for the thumbnail. Only HTTP(S) is supported.
-        height: int
-            The height of the thumbnail.
-        width: int
-            The width of the thumbnail.
         """
 
         self._thumbnail = {
-            'url': url
+            'url': str(url)
         }
 
-        if height is not None:
+        return self
-            self._thumbnail['height'] = height
-
-        if width is not None:
-            self._thumbnail['width'] = width
 
     @property
     def video(self):
@@ -271,7 +277,7 @@ class Embed:
         - ``height`` for the video height.
         - ``width`` for the video width.
 
-        If the attribute cannot be accessed then ``None`` is returned.
+        If the attribute has no value then :attr:`Empty` is returned.
         """
         return EmbedProxy(getattr(self, '_video', {}))
 
@@ -281,7 +287,7 @@ class Embed:
 
         The only attributes that might be accessed are ``name`` and ``url``.
 
-        If the attribute cannot be accessed then ``None`` is returned.
+        If the attribute has no value then :attr:`Empty` is returned.
         """
         return EmbedProxy(getattr(self, '_provider', {}))
 
@@ -291,13 +297,16 @@ class Embed:
 
         See :meth:`set_author` for possible values you can access.
 
-        If the attribute cannot be accessed then ``None`` is returned.
+        If the attribute has no value then :attr:`Empty` is returned.
         """
         return EmbedProxy(getattr(self, '_author', {}))
 
-    def set_author(self, *, name, url=None, icon_url=None):
+    def set_author(self, *, name, url=EmptyEmbed, icon_url=EmptyEmbed):
         """Sets the author for the embed content.
 
+        This function returns the class instance to allow for fluent-style
+        chaining.
+
         Parameters
         -----------
         name: str
@@ -309,15 +318,16 @@ class Embed:
         """
 
         self._author = {
-            'name': name
+            'name': str(name)
         }
 
-        if url is not None:
+        if url is not EmptyEmbed:
-            self._author['url'] = url
+            self._author['url'] = str(url)
 
-        if icon_url is not None:
+        if icon_url is not EmptyEmbed:
-            self._author['icon_url'] = icon_url
+            self._author['icon_url'] = str(icon_url)
 
+        return self
 
     @property
     def fields(self):
@@ -325,13 +335,16 @@ class Embed:
 
         See :meth:`add_field` for possible values you can access.
 
-        If the attribute cannot be accessed then ``None`` is returned.
+        If the attribute has no value then :attr:`Empty` is returned.
         """
         return [EmbedProxy(d) for d in getattr(self, '_fields', [])]
 
-    def add_field(self, *, name=None, value=None, inline=True):
+    def add_field(self, *, name, value, inline=True):
         """Adds a field to the embed object.
 
+        This function returns the class instance to allow for fluent-style
+        chaining.
+
         Parameters
         -----------
         name: str
@@ -343,19 +356,81 @@ class Embed:
         """
 
         field = {
-            'inline': inline
+            'inline': inline,
+            'name': str(name),
+            'value': str(value)
         }
-        if name is not None:
-            field['name'] = name
-
-        if value is not None:
-            field['value'] = value
 
         try:
             self._fields.append(field)
         except AttributeError:
             self._fields = [field]
 
+        return self
+
+    def clear_fields(self):
+        """Removes all fields from this embed."""
+        try:
+            self._fields.clear()
+        except AttributeError:
+            self._fields = []
+
+    def remove_field(self, index):
+        """Removes a field at a specified index.
+
+        If the index is invalid or out of bounds then the error is
+        silently swallowed.
+
+        .. note::
+
+            When deleting a field by index, the index of the other fields
+            shift to fill the gap just like a regular list.
+
+        Parameters
+        -----------
+        index: int
+            The index of the field to remove.
+        """
+        try:
+            del self._fields[index]
+        except (AttributeError, IndexError):
+            pass
+
+    def set_field_at(self, index, *, name, value, inline=True):
+        """Modifies a field to the embed object.
+
+        The index must point to a valid pre-existing field.
+
+        This function returns the class instance to allow for fluent-style
+        chaining.
+
+        Parameters
+        -----------
+        index: int
+            The index of the field to modify.
+        name: str
+            The name of the field.
+        value: str
+            The value of the field.
+        inline: bool
+            Whether the field should be displayed inline.
+
+        Raises
+        -------
+        IndexError
+            An invalid index was provided.
+        """
+
+        try:
+            field = self._fields[index]
+        except (TypeError, IndexError, AttributeError):
+            raise IndexError('field index out of range')
+
+        field['name'] = str(name)
+        field['value'] = str(value)
+        field['inline'] = inline
+        return self
+
     def to_dict(self):
         """Converts this embed object into a dict."""
 
@@ -373,14 +448,16 @@ class Embed:
         except KeyError:
             pass
         else:
-            result['color'] = colour.value
+            if colour:
+                result['color'] = colour.value
 
         try:
             timestamp = result.pop('timestamp')
         except KeyError:
             pass
         else:
-            result['timestamp'] = timestamp.isoformat()
+            if timestamp:
+                result['timestamp'] = timestamp.isoformat()
 
         # add in the non raw attribute ones
         if self.type: