fix: stop rendering "-0.0 pp" for tiny negative share changes in compare

faircode/report.py

@@ -118,6 +118,12 @@ def _delta(n: int | None) -> str:
     return "not available" if n is None else f"{n:+d}"
 
 
+def _strip_neg_zero(val: float, dp: int = 1) -> float:
+    """Return 0.0 when ``val`` rounds to zero at ``dp`` decimals, so a tiny
+    negative value does not render as a misleading ``-0.0``."""
+    return 0.0 if round(val, dp) == 0 else val
+
+
 def _dataset_score_line(dataset: dict) -> str:
     if dataset["overall_score"] is None:
         return f"{dataset['n_rows']:,} rows · score not measured"
@@ -156,7 +162,8 @@ def compare_to_terminal(cmp: dict) -> str:
             tag = {"appeared": "  (appeared)", "disappeared": "  (disappeared)",
                    "shifted": ""}[g["status"]]
             add(f"  {g['label'][:18]:<18} {g['share_a'] * 100:5.1f}% → "
-                f"{g['share_b'] * 100:5.1f}%  ({g['share_delta'] * 100:+5.1f} pp){tag}")
+                f"{g['share_b'] * 100:5.1f}%  "
+                f"({_strip_neg_zero(g['share_delta'] * 100):+5.1f} pp){tag}")
         if len(cd["groups"]) > DISPLAY_GROUPS:
             add(f"  … and {len(cd['groups']) - DISPLAY_GROUPS} more groups")
         add("")
@@ -345,6 +352,7 @@ def esc(s) -> str:
         return html.escape(str(s))
 
     def signed(val: float | int, dp: int = 1) -> str:
+        val = _strip_neg_zero(val, dp)
         prefix = "+" if val > 0 else ""
         return f"{prefix}{val:.{dp}f}"
 

tests/test_report.py

@@ -361,3 +361,31 @@ def test_compare_reports_unmeasured_score_without_formatting_none():
     assert "Overall score change: not available" in terminal_out
     assert "score change not available" in html_out
     assert "None" not in html_out
+
+
+def test_compare_does_not_render_negative_zero_share_delta():
+    """A tiny negative share_delta that rounds to 0.0 pp must not print as
+    '-0.0 pp' in either the terminal or the HTML compare report."""
+    result = {
+        "score_delta": 0,
+        "a": {"name": "A", "overall_score": 100, "n_rows": 10000, "grade": "A"},
+        "b": {"name": "B", "overall_score": 100, "n_rows": 10000, "grade": "A"},
+        "added_dimensions": [], "removed_dimensions": [], "flags": [],
+        "dimensions": [
+            {
+                "name": "Gender", "kind": "Demographic", "drift_level": "none",
+                "psi": 0.0, "tvd": 0.0,
+                "dimension_score_a": 100, "dimension_score_b": 100,
+                "dimension_score_delta": 0,
+                "groups": [
+                    {"label": "Female", "status": "shifted",
+                     "share_a": 0.5, "share_b": 0.4999, "share_delta": -0.0001},
+                    {"label": "Male", "status": "shifted",
+                     "share_a": 0.5, "share_b": 0.5001, "share_delta": 0.0001},
+                ],
+            }
+        ],
+    }
+
+    assert "-0.0 pp" not in compare_to_terminal(result)
+    assert "-0.0 pp" not in compare_to_html(result)