lib: Replaced __cmp__ method with compensating methods for Python3 fu…

…nctionality (#4684)

* updated cmp

* updated gt

* removed cmp

.flake8

@@ -39,9 +39,6 @@ per-file-ignores =
     gui/wxpython/timeline/g.gui.timeline.py: E501
     # Generated file
     gui/wxpython/menustrings.py: E501
-    # F821 undefined name 'cmp'
-    # https://github.com/OSGeo/grass/issues/1809
-    python/grass/pydispatch/saferef.py: F821
     # C wrappers call libgis.G_gisinit before importing other modules.
     # TODO: Is this really needed?
     python/grass/pygrass/vector/__init__.py: E402

python/grass/pydispatch/saferef.py

@@ -164,11 +164,20 @@ def __nonzero__(self):
 
     __bool__ = __nonzero__
 
-    def __cmp__(self, other):
-        """Compare with another reference"""
+    def __eq__(self, other):
         if not isinstance(other, self.__class__):
-            return cmp(self.__class__, type(other))
-        return cmp(self.key, other.key)
+            return False
+        return self.key == other.key
+
+    def __lt__(self, other):
+        if not isinstance(other, self.__class__):
+            return self.__class__.__name__ < other.__class__.__name__
+        return self.key < other.key
+
+    def __gt__(self, other):
+        if not isinstance(other, self.__class__):
+            return self.__class__.__name__ > other.__class__.__name__
+        return self.key > other.key
 
     def __call__(self):
         """Return a strong reference to the bound method