Refactor to run in both Python 2.7 and Python 3.6

Refactor to run in both Python 2.7 and Python 3.6. This is important as
python 2.7 is end of life.

I tried to edit as few things as possible in this commit to minimize
conflicts which means the code could be prettier.

Signed-off-by: Viktor Sjölind <viktor@sjolind.se>

ircbot.py

@@ -25,7 +25,14 @@ write simpler bots.
 """
 
 import sys
-from UserDict import UserDict
+
+# UserDict is moved to collections in Python3
+# In order to support Python 2.7 this has to be imported
+# in the following way
+try:
+    from UserDict import UserDict
+except ImportError:
+    from collections import UserDict
 
 from irclib import SimpleIRCClient
 from irclib import nm_to_n, irc_lower, all_events
@@ -160,7 +167,7 @@ class SingleServerIRCBot(SimpleIRCClient):
         """[Internal]"""
         before = nm_to_n(e.source())
         after = e.target()
-        for ch in self.channels.values():
+        for ch in list(self.channels.values()):
             if ch.has_user(before):
                 ch.change_nick(before, after)
 
@@ -177,7 +184,7 @@ class SingleServerIRCBot(SimpleIRCClient):
     def _on_quit(self, c, e):
         """[Internal]"""
         nick = nm_to_n(e.source())
-        for ch in self.channels.values():
+        for ch in list(self.channels.values()):
             if ch.has_user(nick):
                 ch.remove_user(nick)
 
@@ -283,8 +290,6 @@ class IRCDict:
         del self.canon_keys[ck]
     def __iter__(self):
         return iter(self.data)
-    def __contains__(self, key):
-        return self.has_key(key)
     def clear(self):
         self.data.clear()
         self.canon_keys.clear()
@@ -294,15 +299,15 @@ class IRCDict:
         import copy
         return copy.copy(self)
     def keys(self):
-        return self.data.keys()
+        return list(self.data.keys())
     def items(self):
-        return self.data.items()
+        return list(self.data.items())
     def values(self):
-        return self.data.values()
+        return list(self.data.values())
     def has_key(self, key):
         return irc_lower(key) in self.canon_keys
     def update(self, dict):
-        for k, v in dict.items():
+        for k, v in list(dict.items()):
             self.data[k] = v
     def get(self, key, failobj=None):
         return self.data.get(key, failobj)
@@ -322,16 +327,16 @@ class Channel:
 
     def users(self):
         """Returns an unsorted list of the channel's users."""
-        return self.userdict.keys()
+        return list(self.userdict.keys())
 
     def opers(self):
         """Returns an unsorted list of the channel's operators."""
-        return self.operdict.keys()
+        return list(self.operdict.keys())
 
     def voiced(self):
         """Returns an unsorted list of the persons that have voice
         mode set in the channel."""
-        return self.voiceddict.keys()
+        return list(self.voiceddict.keys())
 
     def has_user(self, nick):
         """Check whether the channel has a user."""