A test suite for binary operators, disguised as a rational number

class.

Lib/test/test_binop.py

+"""Tests for binary operators on subtypes of built-in types."""
+
+import test_support
+import unittest
+
+class getset(object):
+
+    """Define a get/set attribute descriptor.
+
+    This will eventually become a built-in."""
+
+    def __init__(self, get, set=None):
+        self.__get = get
+        self.__set = set
+
+    def __get__(self, inst, type=None):
+        return self.__get(inst)
+
+    def __set__(self, inst, value):
+        if self.__set is None:
+            raise AttributeError, "this attribute is read-only"
+        return self.__set(inst, value)
+
+def gcd(a, b):
+    """Greatest common divisor using Euclid's algorithm."""
+    while a:
+        a, b = b%a, a
+    return b
+
+def isint(x):
+    """Test whether an object is an instance of int or long."""
+    return isinstance(x, int) or isinstance(x, long)
+
+def isnum(x):
+    """Test whether an object is an instance of a built-in numeric type."""
+    for T in int, long, float, complex:
+        if isinstance(x, T):
+            return 1
+    return 0
+
+def isRat(x):
+    """Test wheter an object is an instance of the Rat class."""
+    return isinstance(x, Rat)
+
+class Rat(object):
+
+    """Rational number implemented as a normalized pair of longs."""
+
+    __slots__ = ['_Rat__num', '_Rat__den']
+
+    def __init__(self, num=0L, den=1L):
+        """Constructor: Rat([num[, den]]).
+
+        The arguments must be ints or longs, and default to (0, 1)."""
+        if not isint(num):
+            raise TypeError, "Rat numerator must be int or long (%r)" % num
+        if not isint(den):
+            raise TypeError, "Rat denominator must be int or long (%r)" % den
+        # But the zero is always on
+        if den == 0:
+            raise ZeroDivisionError, "zero denominator"
+        g = gcd(den, num)
+        self.__num = long(num/g)
+        self.__den = long(den/g)
+
+    def _get_num(self):
+        """Accessor function for read-only 'num' attribute of Rat."""
+        return self.__num
+    num = getset(_get_num, None)
+
+    def _get_den(self):
+        """Accessor function for read-only 'den' attribute of Rat."""
+        return self.__den
+    den = getset(_get_den, None)
+
+    def __repr__(self):
+        """Convert a Rat to an string resembling a Rat constructor call."""
+        return "Rat(%d, %d)" % (self.__num, self.__den)
+
+    def __str__(self):
+        """Convert a Rat to a string resembling a decimal numeric value."""
+        return str(float(self))
+
+    def __float__(self):
+        """Convert a Rat to a float."""
+        return self.__num*1.0/self.__den
+
+    def __int__(self):
+        """Convert a Rat to an int; self.den must be 1."""
+        if self.__den == 1:
+            try:
+                return int(self.__num)
+            except OverflowError:
+                raise OverflowError, ("%s too large to convert to int" %
+                                      repr(self))
+        raise ValueError, "can't convert %s to int" % repr(self)
+
+    def __long__(self):
+        """Convert a Rat to an long; self.den must be 1."""
+        if self.__den == 1:
+            return long(self.__num)
+        raise ValueError, "can't convert %s to long" % repr(self)
+
+    def __add__(self, other):
+        """Add two Rats, or a Rat and a number."""
+        if isint(other):
+            other = Rat(other)
+        if isRat(other):
+            return Rat(self.__num*other.__den + other.__num*self.__den,
+                       self.__den*other.__den)
+        if isnum(other):
+            return float(self) + other
+        return NotImplemented
+
+    __radd__ = __add__
+
+    def __sub__(self, other):
+        """Subtract two Rats, or a Rat and a number."""
+        if isint(other):
+            other = Rat(other)
+        if isRat(other):
+            return Rat(self.__num*other.__den - other.__num*self.__den,
+                       self.__den*other.__den)
+        if isnum(other):
+            return float(self) - other
+        return NotImplemented
+
+    def __rsub__(self, other):
+        """Subtract two Rats, or a Rat and a number (reversed args)."""
+        if isint(other):
+            other = Rat(other)
+        if isRat(other):
+            return Rat(other.__num*self.__den - self.__num*other.__den,
+                       self.__den*other.__den)
+        if isnum(other):
+            return other - float(self)
+        return NotImplemented
+
+    def __mul__(self, other):
+        """Multiply two Rats, or a Rat and a number."""
+        if isRat(other):
+            return Rat(self.__num*other.__num, self.__den*other.__den)
+        if isint(other):
+            return Rat(self.__num*other, self.__den)
+        if isnum(other):
+            return float(self)*other
+        return NotImplemented
+
+    __rmul__ = __mul__
+
+    def __truediv__(self, other):
+        """Divide two Rats, or a Rat and a number."""
+        if isRat(other):
+            return Rat(self.__num*other.__den, self.__den*other.__num)
+        if isint(other):
+            return Rat(self.__num, self.__den*other)
+        if isnum(other):
+            return float(self) / other
+        return NotImplemented
+
+    __div__ = __truediv__
+
+    def __rtruediv__(self, other):
+        """Divide two Rats, or a Rat and a number (reversed args)."""
+        if isRat(other):
+            return Rat(other.__num*self.__den, other.__den*self.__num)
+        if isint(other):
+            return Rat(other*self.__den, self.__num)
+        if isnum(other):
+            return other / float(self)
+        return NotImplemented
+
+    __rdiv__ = __rtruediv__
+
+    def __floordiv__(self, other):
+        """Divide two Rats, returning the floored result."""
+        if isint(other):
+            other = Rat(other)
+        elif not isRat(other):
+            return NotImplemented
+        x = self/other
+        return x.__num // x.__den
+
+    def __rfloordiv__(self, other):
+        """Divide two Rats, returning the floored result (reversed args)."""
+        x = other/self
+        return x.__num // x.__den
+
+    def __divmod__(self, other):
+        """Divide two Rats, returning quotient and remainder."""
+        if isint(other):
+            other = Rat(other)
+        elif not isRat(other):
+            return NotImplemented
+        x = self//other
+        return (x, self - other * x)
+
+    def __rdivmod__(self, other):
+        "Divide two Rats, returning quotient and remainder (reversed args)."""
+        if isint(other):
+            other = Rat(other)
+        elif not isRat(other):
+            return NotImplemented
+        return divmod(other, self)
+
+    def __mod__(self, other):
+        """Take one Rat modulo another."""
+        return divmod(self, other)[1]
+
+    def __rmod__(self, other):
+        """Take one Rat modulo another (reversed args)."""
+        return divmod(other, self)[1]
+
+    def __eq__(self, other):
+        """Compare two Rats for equality."""
+        if isint(other):
+            return self.__den == 1 and self.__num == other
+        if isRat(other):
+            return self.__num == other.__num and self.__den == other.__den
+        if isnum(other):
+            return float(self) == other
+        return NotImplemented
+
+    def __ne__(self, other):
+        """Compare two Rats for inequality."""
+        return not self == other
+
+class RatTestCase(unittest.TestCase):
+    """Unit tests for Rat class and its support utilities."""
+
+    def test_gcd(self):
+        self.assertEqual(gcd(10, 12), 2)
+        self.assertEqual(gcd(10, 15), 5)
+        self.assertEqual(gcd(10, 11), 1)
+        self.assertEqual(gcd(100, 15), 5)
+        self.assertEqual(gcd(-10, 2), -2)
+        self.assertEqual(gcd(10, -2), 2)
+        self.assertEqual(gcd(-10, -2), -2)
+        for i in range(1, 20):
+            for j in range(1, 20):
+                self.assert_(gcd(i, j) > 0)
+                self.assert_(gcd(-i, j) < 0)
+                self.assert_(gcd(i, -j) > 0)
+                self.assert_(gcd(-i, -j) < 0)
+
+    def test_constructor(self):
+        a = Rat(10, 15)
+        self.assertEqual(a.num, 2)
+        self.assertEqual(a.den, 3)
+        a = Rat(10L, 15L)
+        self.assertEqual(a.num, 2)
+        self.assertEqual(a.den, 3)
+        a = Rat(10, -15)
+        self.assertEqual(a.num, -2)
+        self.assertEqual(a.den, 3)
+        a = Rat(-10, 15)
+        self.assertEqual(a.num, -2)
+        self.assertEqual(a.den, 3)
+        a = Rat(-10, -15)
+        self.assertEqual(a.num, 2)
+        self.assertEqual(a.den, 3)
+        a = Rat(7)
+        self.assertEqual(a.num, 7)
+        self.assertEqual(a.den, 1)
+        try:
+            a = Rat(1, 0)
+        except ZeroDivisionError:
+            pass
+        else:
+            self.fail("Rat(1, 0) didn't raise ZeroDivisionError")
+        for bad in "0", 0.0, 0j, (), [], {}, None, Rat, unittest:
+            try:
+                a = Rat(bad)
+            except TypeError:
+                pass
+            else:
+                self.fail("Rat(%r) didn't raise TypeError" % bad)
+            try:
+                a = Rat(1, bad)
+            except TypeError:
+                pass
+            else:
+                self.fail("Rat(1, %r) didn't raise TypeError" % bad)
+
+    def test_add(self):
+        self.assertEqual(Rat(2, 3) + Rat(1, 3), 1)
+        self.assertEqual(Rat(2, 3) + 1, Rat(5, 3))
+        self.assertEqual(1 + Rat(2, 3), Rat(5, 3))
+        self.assertEqual(1.0 + Rat(1, 2), 1.5)
+        self.assertEqual(Rat(1, 2) + 1.0, 1.5)
+
+    def test_sub(self):
+        self.assertEqual(Rat(7, 2) - Rat(7, 5), Rat(21, 10))
+        self.assertEqual(Rat(7, 5) - 1, Rat(2, 5))
+        self.assertEqual(1 - Rat(3, 5), Rat(2, 5))
+        self.assertEqual(Rat(3, 2) - 1.0, 0.5)
+        self.assertEqual(1.0 - Rat(1, 2), 0.5)
+
+    def test_mul(self):
+        self.assertEqual(Rat(2, 3) * Rat(5, 7), Rat(10, 21))
+        self.assertEqual(Rat(10, 3) * 3, 10)
+        self.assertEqual(3 * Rat(10, 3), 10)
+        self.assertEqual(Rat(10, 5) * 0.5, 1.0)
+        self.assertEqual(0.5 * Rat(10, 5), 1.0)
+
+    def test_div(self):
+        self.assertEqual(Rat(10, 3) / Rat(5, 7), Rat(14, 3))
+        self.assertEqual(Rat(10, 3) / 3, Rat(10, 9))
+        self.assertEqual(2 / Rat(5), Rat(2, 5))
+        self.assertEqual(3.0 * Rat(1, 2), 1.5)
+        self.assertEqual(Rat(1, 2) * 3.0, 1.5)
+
+    def test_floordiv(self):
+        self.assertEqual(Rat(10) // Rat(4), 2)
+        self.assertEqual(Rat(10, 3) // Rat(4, 3), 2)
+        self.assertEqual(Rat(10) // 4, 2)
+        self.assertEqual(10 // Rat(4), 2)
+
+    def test_eq(self):
+        self.assertEqual(Rat(10), Rat(20, 2))
+        self.assertEqual(Rat(10), 10)
+        self.assertEqual(10, Rat(10))
+        self.assertEqual(Rat(10), 10.0)
+        self.assertEqual(10.0, Rat(10))
+
+    def test_future_div(self):
+        exec future_test
+
+    # XXX Ran out of steam; TO DO: divmod, div, future division
+
+future_test = """
+from __future__ import division
+self.assertEqual(Rat(10, 3) / Rat(5, 7), Rat(14, 3))
+self.assertEqual(Rat(10, 3) / 3, Rat(10, 9))
+self.assertEqual(2 / Rat(5), Rat(2, 5))
+self.assertEqual(3.0 * Rat(1, 2), 1.5)
+self.assertEqual(Rat(1, 2) * 3.0, 1.5)
+"""
+
+test_support.run_unittest(RatTestCase)