raise custom exception to clarify FileNotFoundError

.travis.yml

@@ -7,9 +7,6 @@ matrix:
     - name: Check black formatting
       python: 3.7
       env: TOXENV=black
-    - name: Check flake8 on Python 2
-      python: 2.7
-      env: TOXENV=flake8
     - name: Check flake8 on Python 3
       python: 3.7
       env: TOXENV=flake8

faculty_distributed/manager.py

@@ -8,6 +8,14 @@
 from faculty import client
 
 
+class JobOutputNotFoundError(Exception):
+    """Raised when the output of a job has not been saved. This error is likely
+    to have been raised due to a failed job.
+    """
+
+    pass
+
+
 class FacultyJobExecutor:
     """
     Run generic python function in parallel on Faculty Jobs
@@ -107,11 +115,16 @@ def _collect_output(self, args_sequence):
         """
         out = []
         for i in range(len(args_sequence)):
-            with open(
-                os.path.join(self.tmpdir, "output/out_{}.pkl".format(i)), "rb"
-            ) as f:
-                out.append(cloudpickle.load(f))
-
+            filepath = os.path.join(self.tmpdir, "output/out_{}.pkl".format(i))
+            try:
+                with open(filepath, "rb",) as f:
+                    out.append(cloudpickle.load(f))
+            except FileNotFoundError:
+                raise JobOutputNotFoundError(
+                    "No such file: '{}'. This error is likely to have been "
+                    "raised due to a failed job. Check the Jobs history for "
+                    "further details.".format(filepath)
+                )
         return out
 
     def _make_dirs(self):

tox.ini

@@ -11,6 +11,6 @@ commands =
 [testenv:black]
 skip_install = True
 deps =
-    black==19.3b0
+    black==19.10b0
 commands =
     black {posargs:--check .}