Fix build breakage due to soft torch import (#7790)

.travis.yml

@@ -150,7 +150,7 @@ matrix:
         - if [ $RAY_CI_LINUX_WHEELS_AFFECTED != "1" ]; then exit; fi
 
         # Explicitly sleep 60 seconds for logs to go through
-        - ./ci/travis/test-wheels.sh || cat /tmp/ray/session_latest/logs/* || sleep 60 || false
+        - ./ci/travis/test-wheels.sh || cat /tmp/ray/session_latest/logs/* || (sleep 60 && false)
       cache: false
 
     # Build MacOS wheels.
@@ -168,7 +168,7 @@ matrix:
         - if [ $RAY_CI_MACOS_WHEELS_AFFECTED != "1" ]; then exit; fi
 
         # Explicitly sleep 60 seconds for logs to go through
-        - ./ci/travis/test-wheels.sh || cat /tmp/ray/session_latest/logs/* || sleep 60 || false
+        - ./ci/travis/test-wheels.sh || cat /tmp/ray/session_latest/logs/* || (sleep 60 && false)
 
     # RLlib: Learning tests (from rllib/tuned_examples/regression_tests/*.yaml).
     - os: linux

rllib/utils/framework.py

@@ -99,6 +99,17 @@ def try_import_tfp(error=False):
         return None
 
 
+# Fake module for torch.nn.
+class NNStub:
+    pass
+
+
+# Fake class for torch.nn.Module to allow it to be inherited from.
+class ModuleStub:
+    def __init__(self, *a, **kw):
+        raise ImportError("Could not import `torch`.")
+
+
 def try_import_torch(error=False):
     """
     Args:
@@ -118,7 +129,10 @@ def try_import_torch(error=False):
     except ImportError as e:
         if error:
             raise e
-        return None, None
+
+        nn = NNStub()
+        nn.Module = ModuleStub
+        return None, nn
 
 
 def get_variable(value, framework="tf", tf_name="unnamed-variable"):