rate: Add Rate.convert method.

oxrlib/rate.py

@@ -1,4 +1,5 @@
 import datetime
+import decimal
 import functools
 import json
 
@@ -34,14 +35,21 @@ class Rate:
     def deserialize_timestamp(cls, value):
         return datetime.datetime.fromtimestamp(value)
 
+    @classmethod
+    def serialize_rates(cls, rates):
+        return {code: float(rates[code]) for code in rates}
+
     @classmethod
     def serialize_timestamp(cls, value):
         return int(value.timestamp())
 
     @classmethod
     def from_json_file(cls, json_file):
-        response = json.load(json_file)
+        response = json.load(json_file, parse_float=decimal.Decimal)
         return cls(**response)
 
+    def convert(self, amount, from_currency, to_currency):
+        return amount * self.rates[to_currency] / self.rates[from_currency]
+
     def serialize(self):
         return dict(self.walk_fields(functools.partial(getattr, self), 'serialize'))

tests/historical1.json

@@ -6,6 +6,7 @@
     "rates": {
         "AED": 3.67246,
         "ALL": 144.529793,
-        "ANG": 1.79
+        "ANG": 1.79,
+        "USD": 1
     }
 }

tests/test_Rate.py

@@ -1,4 +1,5 @@
 import datetime
+import decimal
 import io
 import json
 
@@ -7,6 +8,9 @@ from . import relpath
 import oxrlib.rate
 import pytest
 
+HIST1_AED_RATE = decimal.Decimal('3.67246')
+HIST1_ALL_RATE = decimal.Decimal('144.529793')
+
 @pytest.fixture
 def historical1_rate():
     with open(relpath('historical1.json').as_posix()) as rate_file:
@@ -21,3 +25,7 @@ def test_serialize(historical1_rate):
         expected = json.load(rate_file)
     assert expected == historical1_rate.serialize()
 
+def test_convert(historical1_rate):
+    assert historical1_rate.convert(2, 'USD', 'ALL') == (2 * HIST1_ALL_RATE)
+    assert historical1_rate.convert(10, 'AED', 'USD') == (10 / HIST1_AED_RATE)
+    assert historical1_rate.convert(1, 'AED', 'ALL') == (HIST1_ALL_RATE / HIST1_AED_RATE)