add currency pair class

xexe/currency_pair.py

@@ -0,0 +1,19 @@
+from money.currency import Currency
+
+
+class CurrencyPair:
+    """Two currencies with directionality (from->to)."""
+
+    def __init__(
+        self, from_currency: Currency, to_currency: Currency
+    ) -> "CurrencyPair":
+        self.from_currency = from_currency
+        self.to_currency = to_currency
+
+    def __str__(self):
+        return str(self.from_currency) + str(self.to_currency)
+
+    def get_reverse_pair(self) -> "CurrencyPair":
+        return CurrencyPair(
+            from_currency=self.to_currency, to_currency=self.from_currency
+        )