Fix slurm execution (#864)

* do not assert that SLURM_ARRAY_JOB_ID is always set, because it is not

* fix order

* update changelog

Author: daniel-wer

cluster_tools/Changelog.md

@@ -16,6 +16,7 @@ For upgrade instructions, please check the respective *Breaking Changes* section
 ### Changed
 
 ### Fixed
+- Fixed the execution of non-array jobs using slurm. [#864](https://github.com/scalableminds/webknossos-libs/pull/864)
 
 
 ## [0.11.3](https://github.com/scalableminds/webknossos-libs/releases/tag/v0.11.3) - 2023-02-06

cluster_tools/cluster_tools/schedulers/slurm.py

@@ -107,10 +107,11 @@ def get_job_array_index() -> Optional[int]:
             return None
 
     @staticmethod
-    def get_job_array_id() -> str:
-        r = os.environ.get("SLURM_ARRAY_JOB_ID")
-        assert r is not None
-        return r
+    def get_job_array_id() -> Optional[str]:
+        try:
+            return os.environ.get("SLURM_ARRAY_JOB_ID")
+        except KeyError:
+            return None
 
     @staticmethod
     def get_current_job_id() -> str:
@@ -131,7 +132,9 @@ def get_job_id_string(cls) -> str:
         # This variable needs to be kept in sync with the job_id_string variable in the
         # inner_submit function.
         job_id_string = (
-            job_id if job_array_index is None else f"{job_array_id}_{job_array_index}"
+            job_id
+            if job_array_id is None or job_array_index is None
+            else f"{job_array_id}_{job_array_index}"
         )
         return job_id_string