More informative stack trace for benchmark data generation (SciTools#6524)

* More informative traceback for benchmark data gen.

* Use subprocess text output for benchmark data gen.

* Clearer error handling code.

* What's New entry.

Author: trexfeathers

benchmarks/benchmarks/generate_data/__init__.py

@@ -59,6 +59,12 @@
 REUSE_DATA = True
 
 
+class DataGenerationError(Exception):
+    """Exception raised for errors during data generation."""
+
+    pass
+
+
 def run_function_elsewhere(func_to_run, *args, **kwargs):
     """Run a given function using the :const:`DATA_GEN_PYTHON` executable.
 
@@ -92,9 +98,19 @@ def run_function_elsewhere(func_to_run, *args, **kwargs):
         f"{func_to_run.__name__}(" + ",".join(func_call_term_strings) + ")"
     )
     python_string = "\n".join([func_string, func_call_string])
-    result = run(
-        [DATA_GEN_PYTHON, "-c", python_string], capture_output=True, check=True
-    )
+
+    try:
+        result = run(
+            [DATA_GEN_PYTHON, "-c", python_string],
+            capture_output=True,
+            check=True,
+            text=True,
+        )
+    except CalledProcessError as error_:
+        # From None 'breaks' the error chain - we don't want the original
+        #  traceback since it is long and confusing.
+        raise DataGenerationError(error_.stderr) from None
+
     return result.stdout
 
 

benchmarks/benchmarks/generate_data/stock.py

@@ -45,7 +45,7 @@ def _external(func_name_, temp_file_dir, **kwargs_):
             temp_file_dir=str(BENCHMARK_DATA),
             **kwargs,
         )
-        Path(actual_path.decode()).replace(save_path)
+        Path(actual_path).replace(save_path)
     return save_path
 
 

docs/src/whatsnew/latest.rst

@@ -107,6 +107,10 @@ This document explains the changes made to Iris for this release
 #. `@trexfeathers`_ added a CI workflow to quickly validate that the
    benchmarking setup is still working. (:pull:`6496`)
 
+#. `@trexfeathers`_ improved the stack trace for errors that occur during
+   benchmark data generation, showing developers the root problem at-a-glance
+   without needing local replication. (:pull:`6524`)
+
 
 .. comment
     Whatsnew author names (@github name) in alphabetical order. Note that,