And it's done!

Python 2 **can** keep using disco, because `disco.util.runner`
shouldn't be automatically imported.

Changelog:
+ Added two keys to the config.
    `commands_prefix_getter`
    `commands_prefix`
+ Added documentation.
+ Added a new utility file, `disco.util.runner`

disco/bot/bot.py

@@ -49,6 +49,9 @@ class BotConfig(Config):
     commands_prefixes : list[string]
         A list of string prefixes that are required for a message to be considered
         for command parsing.
+    commands_prefix_getter : Optional[function]
+        A function which takes in a message object and returns an array of strings
+        (prefixes).
     commands_allow_edit : bool
         If true, the bot will re-parse an edited message if it was the last sent
         message in a channel, and did not previously trigger a command. This is
@@ -92,6 +95,7 @@ class BotConfig(Config):
     }
     commands_prefix = ''
     commands_prefixes = []
+    commands_prefix_getter = None
     commands_allow_edit = True
     commands_level_getter = None
     commands_group_abbrev = True
@@ -407,12 +411,14 @@ class Bot(LoggingClass):
         bool
             Whether any commands where successfully triggered by the message.
         """
+        custom_message_prefixes = self.config.commands_prefix_getter(msg) if self.config.commands_prefix_getter else []
+
         commands = list(self.get_commands_for_message(
             self.config.commands_require_mention,
             self.config.commands_mention_rules,
             self.config.commands_prefix,
             msg,
-            self.config.commands_prefixes,
+            self.config.commands_prefixes + custom_message_prefixes,
         ))
 
         if not len(commands):

docs/bot_tutorial/programmatic_running.md

@@ -52,7 +52,7 @@ def prefix_getter(message):
 bot = runner.bot_creator({
     'token': TOKEN,
     'bot': {
-        'prefix_getter': prefix_getter,
+        'commands_prefix_getter': prefix_getter,
         'require_mention': False,
         'plugins': ['plugins.tutorial']  # this can be anything
     }