BOM Generation: Unifying reference concatenation using more pythonic string join to avoid trailing comma.

eeschema/python_scripts/bom_csv_grouped_by_value.py

@@ -125,15 +125,16 @@ item = 0
 for group in grouped:
     del row[:]
     refs = ""
+    refs_l = []
 
     # Add the reference of every component in the group and keep a reference
     # to the component so that the other data can be filled in once per group
     for component in group:
-        if len(refs) > 0:
-            refs += ", "
-        refs += component.getRef()
+        refs_l.append( component.getRef() )
         c = component
-
+    
+    refs = ", ".join(refs_l)
+    
     # Fill in the component groups common data
     # columns = ['Item', 'Qty', 'Reference(s)', 'Value', 'LibPart', 'Footprint', 'Datasheet', 'DNP'] + sorted(list(columnset))
     item += 1
@@ -155,4 +156,4 @@ for group in grouped:
 f.close()
 
 if not canOpenFile:
-    sys.exit(1)
+    sys.exit(1)