[price] fix multiplication of prices

bitshares/price.py

@@ -238,14 +238,24 @@ class Price(dict):
         a = self.copy()
         if isinstance(other, Price):
             # Rotate/invert other
-            if self["quote"]["symbol"] in other.symbols():
-                other = other.as_quote(self["quote"]["symbol"])
-            elif self["base"]["symbol"] in other.symbols():
-                other = other.as_quote(self["base"]["symbol"])
-            else:
+            if (
+                self["quote"]["symbol"] not in other.symbols() and
+                self["base"]["symbol"] not in other.symbols()
+            ):
                 raise InvalidAssetException
-            a["base"] = Amount(float(self["base"] * other["base"]), other["base"]["symbol"])
-            a["quote"] = Amount(float(self["quote"] * other["quote"]), self["quote"]["symbol"])
+
+            # base/quote = a/b
+            # a/b * b/c = a/c
+            a = self.copy()
+            if self["quote"]["symbol"] == other["base"]["symbol"]:
+                a["base"] = Amount(float(self["base"]) * float(other["base"]), self["base"]["symbol"])
+                a["quote"] = Amount(float(self["quote"]) * float(other["quote"]), other["quote"]["symbol"])
+            # a/b * c/a =  c/b
+            elif self["base"]["symbol"] == other["quote"]["symbol"]:
+                a["base"] = Amount(float(self["base"]) * float(other["base"]), other["base"]["symbol"])
+                a["quote"] = Amount(float(self["quote"]) * float(other["quote"]), self["quote"]["symbol"])
+            else:
+                raise ValueError("Wrong rotation of prices")
         elif isinstance(other, Amount):
             assert other["asset"]["id"] == self["quote"]["asset"]["id"]
             a = other.copy() * self["price"]

tests/test_price.py

@@ -35,14 +35,14 @@ class Testcases(unittest.TestCase):
 
     def test_multiplication(self):
         p1 = Price(10.0, "USD/GOLD")
-        p2 = Price(5.0, "USD/EUR")
+        p2 = Price(5.0, "EUR/USD")
         p3 = p1 * p2
         p4 = p3.as_base("GOLD")
 
         self.assertEqual(p4["quote"]["symbol"], "EUR")
         self.assertEqual(p4["base"]["symbol"], "GOLD")
-        # 10 USD/GOLD * 0.2 EUR/USD = 2 EUR/GOLD = 0.5 GOLD/EUR
-        self.assertEqual(float(p4), 0.5)
+        # 10 USD/GOLD * 0.2 EUR/USD = 50 EUR/GOLD = 0.02 GOLD/EUR
+        self.assertEqual(float(p4), 0.02)
 
         # Inline multiplication
         p5 = p1
@@ -50,8 +50,8 @@ class Testcases(unittest.TestCase):
         p4 = p5.as_base("GOLD")
         self.assertEqual(p4["quote"]["symbol"], "EUR")
         self.assertEqual(p4["base"]["symbol"], "GOLD")
-        # 10 USD/GOLD * 0.2 EUR/USD = 2 EUR/GOLD = 0.5 GOLD/EUR
-        self.assertEqual(float(p4), 0.5)
+        # 10 USD/GOLD * 0.2 EUR/USD = 2 EUR/GOLD = 0.02 GOLD/EUR
+        self.assertEqual(float(p4), 0.02)
 
     def test_div(self):
         p1 = Price(10.0, "USD/GOLD")