Use attrs, to remove verbose __init__ and __repr__ methods

Backwards compatibility is strictly preserved in `__init__`, including parameter names, defaults and position. Whenever that's difficult using `attrs`, the custom `__init__` is kept instead (for the time being).

`__repr__` methods have changed to the format `attrs` use, but people don't rely on this for anything other than debug output, so it shouldn't be a problem.

fbchat/_group.py

@@ -1,28 +1,32 @@
 # -*- coding: UTF-8 -*-
 from __future__ import unicode_literals
 
+import attr
 from ._thread import ThreadType, Thread
 
 
+@attr.s(cmp=False, init=False)
 class Group(Thread):
     """Represents a Facebook group. Inherits `Thread`"""
 
     #: Unique list (set) of the group thread's participant user IDs
-    participants = None
+    participants = attr.ib(factory=set, converter=lambda x: set() if x is None else x)
     #: A dict, containing user nicknames mapped to their IDs
-    nicknames = None
+    nicknames = attr.ib(factory=dict, converter=lambda x: {} if x is None else x)
     #: A :class:`ThreadColor`. The groups's message color
-    color = None
+    color = attr.ib(None)
     #: The groups's default emoji
-    emoji = None
+    emoji = attr.ib(None)
     # Set containing user IDs of thread admins
-    admins = None
+    admins = attr.ib(factory=set, converter=lambda x: set() if x is None else x)
     # True if users need approval to join
-    approval_mode = None
+    approval_mode = attr.ib(None)
     # Set containing user IDs requesting to join
-    approval_requests = None
+    approval_requests = attr.ib(
+        factory=set, converter=lambda x: set() if x is None else x
+    )
     # Link for joining group
-    join_link = None
+    join_link = attr.ib(None)
 
     def __init__(
         self,
@@ -57,11 +61,12 @@ class Group(Thread):
         self.join_link = join_link
 
 
+@attr.s(cmp=False, init=False)
 class Room(Group):
     """Deprecated. Use :class:`Group` instead"""
 
     # True is room is not discoverable
-    privacy_mode = None
+    privacy_mode = attr.ib(None)
 
     def __init__(self, uid, privacy_mode=None, **kwargs):
         super(Room, self).__init__(uid, **kwargs)