finiterect-constant-driving: sort slice labels for deterministic output

misc/finiterectlat-constant-driving.py

@@ -54,6 +54,8 @@ eh = eV/hbar
 # Check slice ranges and generate all corresponding combinations
 slicepairs = []
 slicelabels = set(a.xslice.keys())  | set(a.yslice.keys())
+slicelabels = sorted(slicelabels, key= lambda l:
+        '.None' if l is None else str(l))
 for label in slicelabels:
     rowslices = a.xslice.get(label, None)
     colslices = a.yslice.get(label, None)