fix: add exponential backoff retry for yfinance rate limits (#426)

tradingagents/dataflows/stockstats_utils.py

@@ -1,10 +1,35 @@
+import time
+import logging
+
 import pandas as pd
 import yfinance as yf
+from yfinance.exceptions import YFRateLimitError
 from stockstats import wrap
 from typing import Annotated
 import os
 from .config import get_config
 
+logger = logging.getLogger(__name__)
+
+
+def yf_retry(func, max_retries=3, base_delay=2.0):
+    """Execute a yfinance call with exponential backoff on rate limits.
+
+    yfinance raises YFRateLimitError on HTTP 429 responses but does not
+    retry them internally. This wrapper adds retry logic specifically
+    for rate limits. Other exceptions propagate immediately.
+    """
+    for attempt in range(max_retries + 1):
+        try:
+            return func()
+        except YFRateLimitError:
+            if attempt < max_retries:
+                delay = base_delay * (2 ** attempt)
+                logger.warning(f"Yahoo Finance rate limited, retrying in {delay:.0f}s (attempt {attempt + 1}/{max_retries})")
+                time.sleep(delay)
+            else:
+                raise
+
 
 def _clean_dataframe(data: pd.DataFrame) -> pd.DataFrame:
     """Normalize a stock DataFrame for stockstats: parse dates, drop invalid rows, fill price gaps."""
@@ -51,14 +76,14 @@ class StockstatsUtils:
         if os.path.exists(data_file):
             data = pd.read_csv(data_file, on_bad_lines="skip")
         else:
-            data = yf.download(
+            data = yf_retry(lambda: yf.download(
                 symbol,
                 start=start_date_str,
                 end=end_date_str,
                 multi_level_index=False,
                 progress=False,
                 auto_adjust=True,
-            )
+            ))
             data = data.reset_index()
             data.to_csv(data_file, index=False)