PERF: Reimplemented remember_last with a weak_lru_cache

which won't leak instances whose methods have been decorated

(specifically DataPortal instances)

MAINT: Not using functools32 anymore

zipline/data/data_portal.py

@@ -31,13 +31,12 @@ from zipline.data.us_equity_loader import (
 )
 
 from zipline.utils import tradingcalendar
-from zipline.utils.compat import lru_cache
 from zipline.utils.math_utils import (
     nansum,
     nanmean,
     nanstd
 )
-from zipline.utils.memoize import remember_last
+from zipline.utils.memoize import remember_last, weak_lru_cache
 from zipline.errors import (
     NoTradeDataAvailableTooEarly,
     NoTradeDataAvailableTooLate,
@@ -1686,7 +1685,7 @@ class DataPortal(object):
         else:
             return [assets] if isinstance(assets, Asset) else []
 
-    @lru_cache(20)
+    @weak_lru_cache(20)
     def _get_minute_count_for_transform(self, ending_minute, days_count):
         # cache size picked somewhat loosely.  this code exists purely to
         # handle deprecated API.