sync from Atlas repo

operator/Interest.java

@@ -0,0 +1,26 @@
+/***
+Compound interest function with ``BigDecimal``
+
+Equivalent in Python:
+
+    def compound_interest(principal, rate, periods):
+        return principal * ((1 + rate) ** periods - 1)
+
+***/
+
+import java.math.BigDecimal;
+
+public class Interest {
+
+    static BigDecimal compoundInterest(BigDecimal principal, BigDecimal rate, int periods) {
+        return principal.multiply(BigDecimal.ONE.add(rate).pow(periods).subtract(BigDecimal.ONE));
+    }
+
+    public static void main(String[] args) {
+        BigDecimal principal = new BigDecimal(1000);
+        BigDecimal rate = new BigDecimal("0.06");
+        int periods = 5;        
+        System.out.println(compoundInterest(principal, rate, periods));
+    }
+
+}

operator/dispatch.py

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+"""
+Experiments with infix operator dispatch
+
+    >>> kadd = KnowsAdd()
+    >>> kadd + 1
+    (<KnowsAdd object>, 1)
+    >>> kadd * 1
+
+"""
+
+
+class KnowsAdd:
+    def __add__(self, other):
+        return self, other
+    def __repr__(self):
+        return '<{} object>'.format(type(self).__name__)
+

operator/interest.py

@@ -0,0 +1,25 @@
+"""
+Compound interest function with ``decimal.Decimal``
+
+"""
+
+def compound_interest(principal, rate, periods):
+    return principal * ((1 + rate) ** periods - 1)
+
+def test(verbose=False):
+    from decimal import Decimal, getcontext
+    getcontext().prec = 8
+    fixture = [(1000, Decimal('0.05'), 1, Decimal('50')),
+               (1000, Decimal('0.10'), 5, Decimal('610.51')),
+               (1000, Decimal('0.10'), 15, Decimal('3177.2482')),
+               (1000, Decimal('0.06'), 5, Decimal('338.2256')),
+              ]
+    for principal, rate, periods, future_value in fixture:
+        computed = compound_interest(principal, rate, periods)
+        if verbose:
+            print('{!r}, {!r}, {!r} -> {!r}'.format(
+                  principal, rate, periods, computed))
+        assert future_value == computed, '{!r} != {!r}'.format(future_value, computed)
+
+if __name__ == '__main__':
+    test(True)