Remove support for on_callback with 3 arguments

ChangeLog.txt

@@ -4,6 +4,8 @@ v1.3.x - 2017-xx-xx
 - **BREAKING** Requires Python 2.7 or 3.4+. Closes #163.
 - **BREAKING** Remove support for SSL without SSLContext (Requires Python 2.7.9+ or 3.2+).
   Closes #115.
+- **BREAKING** on_connect callback is now always called flags. Previously this
+  callback could accepts 3 OR 4 arguments, now it must accepts 4. Closes #197.
 - **BREAKING** tls_insecure_set() must now be called *after* tls_set()
 - Allow username and password to be zero length (as opposed to not being
   present). Closes #80.

src/paho/mqtt/client.py

@@ -2333,19 +2333,10 @@ class Client(object):
 
         with self._callback_mutex:
             if self.on_connect:
-                if sys.version_info[0] < 3:
-                    argcount = self.on_connect.func_code.co_argcount
-                else:
-                    argcount = self.on_connect.__code__.co_argcount
-
-                if argcount == 3:
-                    with self._in_callback:
-                        self.on_connect(self, self._userdata, result)
-                else:
-                    flags_dict = {}
-                    flags_dict['session present'] = flags & 0x01
-                    with self._in_callback:
-                        self.on_connect(self, self._userdata, flags_dict, result)
+                flags_dict = {}
+                flags_dict['session present'] = flags & 0x01
+                with self._in_callback:
+                    self.on_connect(self, self._userdata, flags_dict, result)
 
         if result == 0:
             rc = 0