Remove some Python 2 compatibility code. (#6624)

python/ray/experimental/serve/__init__.py

@@ -1,12 +1,9 @@
-import sys
 from ray.experimental.serve.backend_config import BackendConfig
 from ray.experimental.serve.policy import RoutePolicy
-if sys.version_info < (3, 0):
-    raise ImportError("serve is Python 3 only.")
-
 from ray.experimental.serve.api import (
     init, create_backend, create_endpoint, link, split, get_handle, stat,
     set_backend_config, get_backend_config, accept_batch)  # noqa: E402
+
 __all__ = [
     "init", "create_backend", "create_endpoint", "link", "split", "get_handle",
     "stat", "set_backend_config", "get_backend_config", "BackendConfig",

python/ray/experimental/sgd/tests/test_pytorch_runner.py

@@ -3,18 +3,13 @@ from __future__ import division
 from __future__ import print_function
 
 import numpy as np
-import sys
 import torch
 import torch.nn as nn
 import unittest
+from unittest.mock import MagicMock
 
 from ray.experimental.sgd.pytorch.pytorch_runner import PyTorchRunner
 
-if sys.version_info >= (3, 3):
-    from unittest.mock import MagicMock
-else:
-    from mock import MagicMock
-
 
 class LinearDataset(torch.utils.data.Dataset):
     """y = a * x + b"""