Initial commit

Solutions/7_3/stock.py

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+# stock.py
+
+from structure import Structure
+from validate import String, PositiveInteger, PositiveFloat
+
+class Stock(Structure):
+    name = String()
+    shares = PositiveInteger()
+    price = PositiveFloat()
+
+    @property
+    def cost(self):
+        return self.shares * self.price
+
+    def sell(self, nshares: PositiveInteger):
+        self.shares -= nshares