Merge 36d6a73 into aa6f673

tests.py

@@ -513,6 +513,16 @@ def test_get_by_name():
     """Assert that the Operator class returns operators by name appropriately"""
     assert Operator.get_by_name("SelectKBest").__class__ == TPOTSelectKBest
 
+def test_operator_inheritors_order():
+    """Assert that the Operations.inheritors() always return the same order."""
+    same_order = []
+    for _ in range(10):
+        operators1 = map(lambda op: op.__name__, Operator.inheritors())
+        operators2 = map(lambda op: op.__name__, Operator.inheritors())
+        ordered = all([op1 == op2 for (op1, op2) in zip(operators1, operators2)])
+        same_order.append(ordered)
+
+    assert all(same_order)
 
 def test_gen():
     """Assert that TPOT's gen_grow_safe function returns a pipeline of expected structure"""

tpot/operators/base.py

@@ -122,16 +122,17 @@ def inheritors(cls):
         Returns
         -------
         operators: set
-            Set of all discovered operators that inherit from the base class
+            List of all discovered operators that inherit from the base class
 
         """
-        operators = set()
+        operators = list()
 
         # Search two levels deep and report leaves in inheritance tree
         for operator_type in cls.__subclasses__():
             for operator in operator_type.__subclasses__():
-                operators.add(operator())  # Instantiate class and append
-
+                operators.append(operator())  # Instantiate class and append
+
+        operators = sorted(operators, key=lambda op: op.__name__)
         return operators
 
     @classmethod