Fix _tp() to always return pandas Series (#202)

When amount column is present, _tp() was returning a numpy array instead
of a pandas Series, causing inconsistent behavior in downstream indicators
like MFI. Now both code paths consistently return a Series via to_series().

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: jealous

README.md

@@ -4,7 +4,7 @@
 [![codecov](https://codecov.io/gh/jealous/stockstats/branch/master/graph/badge.svg?token=IFMD1pVJ7T)](https://codecov.io/gh/jealous/stockstats)
 [![pypi](https://img.shields.io/pypi/v/stockstats.svg)](https://pypi.python.org/pypi/stockstats)
 
-VERSION: 0.6.6
+VERSION: 0.6.7
 
 ## Introduction
 

stockstats.py

@@ -969,11 +969,13 @@ def _shifted_cr_sma(self, cr, window):
         cr_sma = self.sma(cr, window)
         return self.s_shift(cr_sma, -int(window / 2.5 + 1))
 
-    def _tp(self):
+    def _tp(self) -> pd.Series:
         if "amount" in self:
-            return self.amount.values / self.volume.values
-        total = self.close.values + self.high.values + self.low.values
-        return self.to_series(total / 3.0)
+            tp = self.amount.values / self.volume.values
+        else:
+            total = self.close.values + self.high.values + self.low.values
+            tp = total / 3.0
+        return self.to_series(tp)
 
     def _get_tp(self, meta: _Meta):
         self[meta.name] = self._tp()

test.py

@@ -728,6 +728,10 @@ def test_mfi(self):
         assert_that(mfi_15.loc[first], near_to(0.5))
         assert_that(mfi_15.loc[last], near_to(0.6733))
 
+    def test_mfi_with_amount(self):
+        mfi = self._supor['mfi']
+        assert_that(mfi.loc[20160817], near_to(0.48265))
+
     def test_ker(self):
         stock = self.get_stock_90days()
         k = stock["ker"]