Fix typing errors in handicap_equations, clarify spec requirements in s_bar

Author: TomHall2020

archeryutils/handicaps/handicap_equations.py

@@ -347,7 +347,7 @@ def sigma_r(
     return sig_r
 
 
-def s_bar(target_specs: dict[float, int], arw_rad: float, sig_r: float):
+def s_bar(target_specs: dict[float, int], arw_rad: float, sig_r: FloatArray) -> FloatArray:
     """Calculate expected score directly from target ring sizes.
 
     Parameters
@@ -371,15 +371,21 @@ def s_bar(target_specs: dict[float, int], arw_rad: float, sig_r: float):
     dividing by overall diameter
     Eg 0.12 / 2 != 3*0.4 / 20
 
+    Assumes that:
+    - target rings are concentric
+    - score decreases monotonically as ring sizes increase
+
     Examples
     --------
     >>> #WA 18m compound triple spot
     >>> specs = {0.02: 10, 0.08: 9, 0.12: 8, 0.16: 7, 0.2: 6}
     >>> _sbar(specs, 9.3e-3, 0.04)
     8.928787288284521 # differs from previous implementation by 1.7763568394002505e-15
     """
-    ring_sizes = sorted(target_specs, key=target_specs.get, reverse=True)
-    ring_scores = sorted(itr.chain(target_specs.values(), [0]), reverse=True)
+    target_specs = dict(sorted(target_specs.items()))
+    ring_sizes = target_specs.keys()
+    ring_scores = list(itr.chain(target_specs.values(), [0]))
+
     score_drops = (inner - outer for inner, outer in itr.pairwise(ring_scores))
     max_score = max(ring_scores)