[GH-165] Add Know Sure Thing support

The Know Sure Thing (KST) is a momentum oscillator developed by
Martin Pring to make rate-of-change readings easier for traders
to interpret.

https://www.investopedia.com/terms/k/know-sure-thing-kst.asp

Formular:
* KST=(RCMA1×1)+(RCMA2×2) + (RCMA3×3)+(RCMA4×4)

Where:
* RCMA1=10-period SMA of 10-period ROC
* RCMA2=10-period SMA of 15-period ROC
* RCMA3=10-period SMA of 20-period ROC
* RCMA4=15-period SMA of 30-period ROC

README.md

@@ -975,6 +975,21 @@ Examples:
 * `df['inertia']` retrieves the inertia of 20 periods linear regression of 14 periods RVGI
 * `df['inertia_10']` retrieves the inertia of 10 periods linear regression of 14 periods RVGI
 
+#### [Know Sure Thing (kst)](https://www.investopedia.com/terms/k/know-sure-thing-kst.asp)
+
+The Know Sure Thing (KST) is a momentum oscillator developed by
+Martin Pring to make rate-of-change readings easier for traders
+to interpret.
+
+Formular:
+* KST=(RCMA #1×1)+(RCMA #2×2) + (RCMA #3×3)+(RCMA #4×4)
+
+Where:
+* RCMA #1=10-period SMA of 10-period ROC
+* RCMA #2=10-period SMA of 15-period ROC
+* RCMA #3=10-period SMA of 20-period ROC
+* RCMA #4=15-period SMA of 30-period ROC
+
 ## Issues
 
 We use [Github Issues](https://github.com/jealous/stockstats/issues) to track

stockstats.py

@@ -1554,6 +1554,33 @@ def _get_inertia(self, meta: _Meta):
         value = self._inertia(meta.int0, meta.int1)
         self[meta.name] = value
 
+    def _kst(self)->pd.Series:
+        """ Know Sure Thing (kst)
+
+        https://www.investopedia.com/terms/k/know-sure-thing-kst.asp
+
+        The Know Sure Thing (KST) is a momentum oscillator developed by
+        Martin Pring to make rate-of-change readings easier for traders
+        to interpret.
+
+        Formular:
+        * KST=(RCMA #1×1)+(RCMA #2×2) + (RCMA #3×3)+(RCMA #4×4)
+
+        where:
+        * RCMA #1=10-period SMA of 10-period ROC
+        * RCMA #2=10-period SMA of 15-period ROC
+        * RCMA #3=10-period SMA of 20-period ROC
+        * RCMA #4=15-period SMA of 30-period ROC
+        """
+        ma1 = self.sma(self.roc(self.close, 10), 10)
+        ma2 = self.sma(self.roc(self.close, 15), 10)
+        ma3 = self.sma(self.roc(self.close, 20), 10)
+        ma4 = self.sma(self.roc(self.close, 30), 15)
+        return ma1 + ma2 * 2 + ma3 * 3 + ma4 * 4
+
+    def _get_kst(self, meta: _Meta):
+        self[meta.name] = self._kst()
+
     @staticmethod
     def parse_column_name(name):
         m = re.match(r'(.*)_([\d\-+~,.]+)_(\w+)', name)
@@ -1699,6 +1726,7 @@ def handler(self):
             ('ftr',): self._get_ftr,
             ('rvgi', 'rvgis'): self._get_rvgi,
             ('inertia',): self._get_inertia,
+            ('kst',): self._get_kst,
         }
 
     def __init_not_exist_column(self, key):

test.py

@@ -1037,3 +1037,10 @@ def test_inertia(self):
         inertia10 = stock['inertia_10']
         assert_that(inertia10[20110209], near_to(0.011085))
         assert_that(inertia10[20110210], near_to(-0.014669))
+
+    def test_kst(self):
+        stock = self.get_stock_90days()
+        kst = stock['kst']
+        assert_that(kst[20110117], equal_to(0))
+        assert_that(kst[20110118], near_to(0.063442))
+        assert_that(kst[20110131], near_to(-2.519985))