fix(polymarket): keep a long shot's odds from printing as 0% or 100% (#1598)

- within 1% of 0 or 100, the distance keeps two significant digits: 0.05%, 99.95%

tests/test_polymarket.py

@@ -78,6 +78,19 @@ class PolymarketFormatTests(unittest.TestCase):
         self.assertIn("resolves 2030-12-31", out)
         self.assertIn("1-week -4.5pp", out)  # -0.045 -> -4.5pp
 
+    def test_a_long_shot_is_not_shown_as_impossible_or_certain(self):
+        search = {"events": [{"markets": [
+            _market("Long shot?", 0.003, volume=2_000, end_date="2030-12-31T00:00:00Z"),
+            _market("Near certain?", 0.997, volume=1_000, end_date="2030-12-31T00:00:00Z"),
+            _market("Tick from zero?", 0.0005, volume=900, end_date="2030-12-31T00:00:00Z"),
+            _market("Tick from one?", 0.9995, volume=800, end_date="2030-12-31T00:00:00Z"),
+            _market("All but settled?", 0.9999999, volume=700, end_date="2030-12-31T00:00:00Z"),
+        ]}]}
+        with mock.patch.object(polymarket, "_request", return_value=search):
+            out = polymarket.get_prediction_markets("anything", limit=10)
+        for odds in ("Yes 0.3%", "Yes 99.7%", "Yes 0.05%", "Yes 99.95%", "Yes 99.99999%"):
+            self.assertIn(odds, out)
+
     def test_weekly_change_omitted_when_absent(self):
         # "Open small?" has wk=None -> no 1-week clause on its line.
         with mock.patch.object(polymarket, "_request", return_value=_SEARCH):

tradingagents/dataflows/vendors/polymarket.py

@@ -11,6 +11,7 @@ outcomes (a "Yes" at 0.76 means the market prices a 76% chance).
 """
 import json
 import logging
+import math
 from datetime import UTC, datetime
 
 import requests
@@ -67,6 +68,21 @@ def _is_forward_looking(market: dict, now: datetime) -> bool:
     )
 
 
+def _odds(prob: float) -> str:
+    """A probability as a percentage; within 1% of 0 or 100 its distance from
+    there keeps two significant digits, so 0.05% is not 0% and 99.95% not 100%."""
+    def decimals(distance: float) -> int:
+        return 1 - math.floor(math.log10(distance))
+
+    if 0 < prob < 0.01:
+        percent = prob * 100
+        return f"{percent:.{decimals(percent)}f}".rstrip("0").rstrip(".") + "%"
+    if 0.99 < prob < 1:
+        distance = (1 - prob) * 100
+        return f"{100 - distance:.{decimals(distance)}f}".rstrip("0").rstrip(".") + "%"
+    return f"{prob:.0%}"
+
+
 def get_prediction_markets(topic: str, limit: int | None = None, as_of_date: str | None = None) -> str:
     """Return live prediction-market probabilities for an event topic.
 
@@ -142,7 +158,7 @@ def get_prediction_markets(topic: str, limit: int | None = None, as_of_date: str
             else ""
         )
         lines.append(
-            f"- **{m.get('question')}** — {label} {prob:.0%} "
+            f"- **{m.get('question')}** — {label} {_odds(prob)} "
             f"(${volume:,.0f} volume, resolves {end_date}{wk_str})"
         )