Add Python binding for rabit ops. (#5743)

python-package/xgboost/rabit.py

@@ -56,6 +56,12 @@ def get_world_size():
     return ret
 
 
+def is_distributed():
+    '''If rabit is distributed.'''
+    is_dist = _LIB.RabitIsDistributed()
+    return is_dist
+
+
 def tracker_print(msg):
     """Print message to the tracker.
 
@@ -143,6 +149,14 @@ DTYPE_ENUM__ = {
 }
 
 
+class Op:                     # pylint: disable=too-few-public-methods
+    '''Supported operations for rabit.'''
+    MAX = 0
+    MIN = 1
+    SUM = 2
+    OR = 3
+
+
 def allreduce(data, op, prepare_fun=None):
     """Perform allreduce, return the result.