[tune] Support callable objects in variant generation (#6849)

* minorcallable

* format

python/ray/tune/suggest/variant_generator.py

@@ -2,7 +2,6 @@ import copy
 import logging
 import numpy
 import random
-import types
 
 from ray.tune import TuneError
 from ray.tune.sample import sample_from
@@ -126,7 +125,7 @@ def _generate_variants(spec):
     grid_vars = []
     lambda_vars = []
     for path, value in unresolved.items():
-        if isinstance(value, types.FunctionType):
+        if callable(value):
             lambda_vars.append((path, value))
         else:
             grid_vars.append((path, value))