Remove a pytype: disable by adding some filtering to compare.py.

I noticed when exporting our latest changes to GitHub that we had to add a
disable for an unsupported-operands error. The error seems to be a false
positive, caused by some missing filtering in compare.py.

While I was touching the comparison code, I also fixed a lint warning.

PiperOrigin-RevId: 392545719

pytype/compare.py

@@ -51,8 +51,8 @@ def _is_equality_cmp(op):
 def _compare_constants(op, left, right):
   try:
     return slots.COMPARES[op](left, right)
-  except TypeError:
-    raise CmpTypeError()
+  except TypeError as e:
+    raise CmpTypeError() from e
 
 
 def _compare_primitive_constant(vm, op, left, right):

pytype/errors.py

@@ -440,7 +440,7 @@ def unique_sorted_errors(self):
           #   f("world")  # same error, different backtrace
           # so we'll report this error multiple times with different backtraces.
           continue
-        elif traceback_cmp < 0:  # pytype: disable=unsupported-operands
+        elif traceback_cmp < 0:
           # If the current traceback is shorter, use the current error instead
           # of the previous one.
           errors.remove(previous_error)

pytype/vm.py

@@ -2347,7 +2347,8 @@ def _cmp_rel(self, state, op_name, x, y):
           val = compare.cmp_rel(self, op, b1.data, b2.data)
         except compare.CmpTypeError:
           val = None
-          self.errorlog.unsupported_operands(self.frames, op, x, y)
+          if state.node.HasCombination([b1, b2]):
+            self.errorlog.unsupported_operands(self.frames, op, x, y)
         if val is None:
           leftover_x.AddBinding(b1.data, {b1}, state.node)
           leftover_y.AddBinding(b2.data, {b2}, state.node)