Made the various is_* operations return booleans. This was discussed

with Cawlishaw by mail, and he basically confirmed that to these is_*
operations, there's no need to return Decimal(0) and Decimal(1) if
the language supports the False and True booleans.

Also added a few tests for the these functions in extra.decTest, since
they are mostly untested (apart from the doctests).

Thanks Mark Dickinson

Lib/decimal.py

@@ -679,14 +679,11 @@ class Decimal(object):
         return 0
 
     def __nonzero__(self):
-        """Is the number non-zero?
+        """Return True if self is nonzero; otherwise return False.
 
-        0 if self == 0
+        NaNs and infinities are considered nonzero.
-        1 if self != 0
         """
-        if self._is_special:
+        return self._is_special or self._int[0] != 0
-            return True
-        return sum(self._int) != 0
 
     def __cmp__(self, other):
         other = _convert_other(other)
@@ -2239,15 +2236,18 @@ class Decimal(object):
         return ans
 
     def same_quantum(self, other):
-        """Test whether self and other have the same exponent.
+        """Return True if self and other have the same exponent; otherwise
+        return False.
 
-        same as self._exp == other._exp, except NaN == sNaN
+        If either operand is a special value, the following rules are used:
+           * return True if both operands are infinities
+           * return True if both operands are NaNs
+           * otherwise, return False.
         """
+        other = _convert_other(other, raiseit=True)
         if self._is_special or other._is_special:
-            if self._isnan() or other._isnan():
+            return (self.is_nan() and other.is_nan() or
-                return self._isnan() and other._isnan() and True
+                    self.is_infinite() and other.is_infinite())
-            if self._isinfinity() or other._isinfinity():
-                return self._isinfinity() and other._isinfinity() and True
         return self._exp == other._exp
 
     def _rescale(self, exp, rounding):
@@ -2730,84 +2730,60 @@ class Decimal(object):
         return ans
 
     def is_canonical(self):
-        """Returns 1 if self is canonical; otherwise returns 0."""
+        """Return True if self is canonical; otherwise return False.
-        return Dec_p1
+
+        Currently, the encoding of a Decimal instance is always
+        canonical, so this method returns True for any Decimal.
+        """
+        return True
 
     def is_finite(self):
-        """Returns 1 if self is finite, otherwise returns 0.
+        """Return True if self is finite; otherwise return False.
 
-        For it to be finite, it must be neither infinite nor a NaN.
+        A Decimal instance is considered finite if it is neither
+        infinite nor a NaN.
         """
-        if self._is_special:
+        return not self._is_special
-            return Dec_0
-        else:
-            return Dec_p1
 
     def is_infinite(self):
-        """Returns 1 if self is an Infinite, otherwise returns 0."""
+        """Return True if self is infinite; otherwise return False."""
-        if self._isinfinity():
+        return self._exp == 'F'
-            return Dec_p1
-        else:
-            return Dec_0
 
     def is_nan(self):
-        """Returns 1 if self is qNaN or sNaN, otherwise returns 0."""
+        """Return True if self is a qNaN or sNaN; otherwise return False."""
-        if self._isnan():
+        return self._exp in ('n', 'N')
-            return Dec_p1
-        else:
-            return Dec_0
 
     def is_normal(self, context=None):
-        """Returns 1 if self is a normal number, otherwise returns 0."""
+        """Return True if self is a normal number; otherwise return False."""
-        if self._is_special:
+        if self._is_special or not self:
-            return Dec_0
+            return False
-        if not self:
-            return Dec_0
         if context is None:
             context = getcontext()
-        if context.Emin <= self.adjusted() <= context.Emax:
+        return context.Emin <= self.adjusted() <= context.Emax
-            return Dec_p1
-        else:
-            return Dec_0
 
     def is_qnan(self):
-        """Returns 1 if self is a quiet NaN, otherwise returns 0."""
+        """Return True if self is a quiet NaN; otherwise return False."""
-        if self._isnan() == 1:
+        return self._exp == 'n'
-            return Dec_p1
-        else:
-            return Dec_0
 
     def is_signed(self):
-        """Returns 1 if self is negative, otherwise returns 0."""
+        """Return True if self is negative; otherwise return False."""
-        return Decimal(self._sign)
+        return self._sign == 1
 
     def is_snan(self):
-        """Returns 1 if self is a signaling NaN, otherwise returns 0."""
+        """Return True if self is a signaling NaN; otherwise return False."""
-        if self._isnan() == 2:
+        return self._exp == 'N'
-            return Dec_p1
-        else:
-            return Dec_0
 
     def is_subnormal(self, context=None):
-        """Returns 1 if self is subnormal, otherwise returns 0."""
+        """Return True if self is subnormal; otherwise return False."""
-        if self._is_special:
+        if self._is_special or not self:
-            return Dec_0
+            return False
-        if not self:
-            return Dec_0
         if context is None:
             context = getcontext()
-
+        return self.adjusted() < context.Emin
-        r = self._exp + len(self._int)
-        if r <= context.Emin:
-            return Dec_p1
-        return Dec_0
 
     def is_zero(self):
-        """Returns 1 if self is a zero, otherwise returns 0."""
+        """Return True if self is a zero; otherwise return False."""
-        if self:
+        return not self._is_special and self._int[0] == 0
-            return Dec_0
-        else:
-            return Dec_p1
 
     def _ln_exp_bound(self):
         """Compute a lower bound for the adjusted exponent of self.ln().
@@ -3871,138 +3847,145 @@ class Context(object):
         return a.fma(b, c, context=self)
 
     def is_canonical(self, a):
-        """Returns 1 if the operand is canonical; otherwise returns 0.
+        """Return True if the operand is canonical; otherwise return False.
+
+        Currently, the encoding of a Decimal instance is always
+        canonical, so this method returns True for any Decimal.
 
         >>> ExtendedContext.is_canonical(Decimal('2.50'))
-        Decimal("1")
+        True
         """
-        return Dec_p1
+        return a.is_canonical()
 
     def is_finite(self, a):
-        """Returns 1 if the operand is finite, otherwise returns 0.
+        """Return True if the operand is finite; otherwise return False.
 
-        For it to be finite, it must be neither infinite nor a NaN.
+        A Decimal instance is considered finite if it is neither
+        infinite nor a NaN.
 
         >>> ExtendedContext.is_finite(Decimal('2.50'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_finite(Decimal('-0.3'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_finite(Decimal('0'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_finite(Decimal('Inf'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_finite(Decimal('NaN'))
-        Decimal("0")
+        False
         """
         return a.is_finite()
 
     def is_infinite(self, a):
-        """Returns 1 if the operand is an Infinite, otherwise returns 0.
+        """Return True if the operand is infinite; otherwise return False.
 
         >>> ExtendedContext.is_infinite(Decimal('2.50'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_infinite(Decimal('-Inf'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_infinite(Decimal('NaN'))
-        Decimal("0")
+        False
         """
         return a.is_infinite()
 
     def is_nan(self, a):
-        """Returns 1 if the operand is qNaN or sNaN, otherwise returns 0.
+        """Return True if the operand is a qNaN or sNaN;
+        otherwise return False.
 
         >>> ExtendedContext.is_nan(Decimal('2.50'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_nan(Decimal('NaN'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_nan(Decimal('-sNaN'))
-        Decimal("1")
+        True
         """
         return a.is_nan()
 
     def is_normal(self, a):
-        """Returns 1 if the operand is a normal number, otherwise returns 0.
+        """Return True if the operand is a normal number;
+        otherwise return False.
 
         >>> c = ExtendedContext.copy()
         >>> c.Emin = -999
         >>> c.Emax = 999
         >>> c.is_normal(Decimal('2.50'))
-        Decimal("1")
+        True
         >>> c.is_normal(Decimal('0.1E-999'))
-        Decimal("0")
+        False
         >>> c.is_normal(Decimal('0.00'))
-        Decimal("0")
+        False
         >>> c.is_normal(Decimal('-Inf'))
-        Decimal("0")
+        False
         >>> c.is_normal(Decimal('NaN'))
-        Decimal("0")
+        False
         """
         return a.is_normal(context=self)
 
     def is_qnan(self, a):
-        """Returns 1 if the operand is a quiet NaN, otherwise returns 0.
+        """Return True if the operand is a quiet NaN; otherwise return False.
 
         >>> ExtendedContext.is_qnan(Decimal('2.50'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_qnan(Decimal('NaN'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_qnan(Decimal('sNaN'))
-        Decimal("0")
+        False
         """
         return a.is_qnan()
 
     def is_signed(self, a):
-        """Returns 1 if the operand is negative, otherwise returns 0.
+        """Return True if the operand is negative; otherwise return False.
 
         >>> ExtendedContext.is_signed(Decimal('2.50'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_signed(Decimal('-12'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_signed(Decimal('-0'))
-        Decimal("1")
+        True
         """
         return a.is_signed()
 
     def is_snan(self, a):
-        """Returns 1 if the operand is a signaling NaN, otherwise returns 0.
+        """Return True if the operand is a signaling NaN;
+        otherwise return False.
 
         >>> ExtendedContext.is_snan(Decimal('2.50'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_snan(Decimal('NaN'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_snan(Decimal('sNaN'))
-        Decimal("1")
+        True
         """
         return a.is_snan()
 
     def is_subnormal(self, a):
-        """Returns 1 if the operand is subnormal, otherwise returns 0.
+        """Return True if the operand is subnormal; otherwise return False.
 
         >>> c = ExtendedContext.copy()
         >>> c.Emin = -999
         >>> c.Emax = 999
         >>> c.is_subnormal(Decimal('2.50'))
-        Decimal("0")
+        False
         >>> c.is_subnormal(Decimal('0.1E-999'))
-        Decimal("1")
+        True
         >>> c.is_subnormal(Decimal('0.00'))
-        Decimal("0")
+        False
         >>> c.is_subnormal(Decimal('-Inf'))
-        Decimal("0")
+        False
         >>> c.is_subnormal(Decimal('NaN'))
-        Decimal("0")
+        False
         """
         return a.is_subnormal(context=self)
 
     def is_zero(self, a):
-        """Returns 1 if the operand is a zero, otherwise returns 0.
+        """Return True if the operand is a zero; otherwise return False.
 
         >>> ExtendedContext.is_zero(Decimal('0'))
-        Decimal("1")
+        True
         >>> ExtendedContext.is_zero(Decimal('2.50'))
-        Decimal("0")
+        False
         >>> ExtendedContext.is_zero(Decimal('-0E+2'))
-        Decimal("1")
+        True
         """
         return a.is_zero()
 

Lib/test/test_decimal.py

@@ -95,35 +95,61 @@ RoundingDict = {'ceiling' : ROUND_CEILING, #Maps test-case names to roundings.
 
 # Name adapter to be able to change the Decimal and Context
 # interface without changing the test files from Cowlishaw
-nameAdapter = {'toeng':'to_eng_string',
+nameAdapter = {'and':'logical_and',
-               'tosci':'to_sci_string',
-               'samequantum':'same_quantum',
-               'tointegral':'to_integral_value',
-               'tointegralx':'to_integral_exact',
-               'remaindernear':'remainder_near',
-               'divideint':'divide_int',
-               'squareroot':'sqrt',
                'apply':'_apply',
                'class':'number_class',
                'comparesig':'compare_signal',
                'comparetotal':'compare_total',
                'comparetotmag':'compare_total_mag',
-               'copyabs':'copy_abs',
                'copy':'copy_decimal',
+               'copyabs':'copy_abs',
                'copynegate':'copy_negate',
                'copysign':'copy_sign',
-               'and':'logical_and',
+               'divideint':'divide_int',
-               'or':'logical_or',
-               'xor':'logical_xor',
                'invert':'logical_invert',
+               'iscanonical':'is_canonical',
+               'isfinite':'is_finite',
+               'isinfinite':'is_infinite',
+               'isnan':'is_nan',
+               'isnormal':'is_normal',
+               'isqnan':'is_qnan',
+               'issigned':'is_signed',
+               'issnan':'is_snan',
+               'issubnormal':'is_subnormal',
+               'iszero':'is_zero',
                'maxmag':'max_mag',
                'minmag':'min_mag',
                'nextminus':'next_minus',
                'nextplus':'next_plus',
                'nexttoward':'next_toward',
+               'or':'logical_or',
                'reduce':'normalize',
+               'remaindernear':'remainder_near',
+               'samequantum':'same_quantum',
+               'squareroot':'sqrt',
+               'toeng':'to_eng_string',
+               'tointegral':'to_integral_value',
+               'tointegralx':'to_integral_exact',
+               'tosci':'to_sci_string',
+               'xor':'logical_xor',
               }
 
+# The following functions return True/False rather than a Decimal instance
+
+LOGICAL_FUNCTIONS = (
+    'is_canonical',
+    'is_finite',
+    'is_infinite',
+    'is_nan',
+    'is_normal',
+    'is_qnan',
+    'is_signed',
+    'is_snan',
+    'is_subnormal',
+    'is_zero',
+    'same_quantum',
+    )
+
 # For some operations (currently exp, ln, log10, power), the decNumber
 # reference implementation imposes additional restrictions on the
 # context and operands.  These restrictions are not part of the
@@ -321,7 +347,7 @@ class DecimalTest(unittest.TestCase):
             print "--", self.context
         try:
             result = str(funct(*vals))
-            if fname == 'same_quantum':
+            if fname in LOGICAL_FUNCTIONS:
                 result = str(int(eval(result))) # 'True', 'False' -> '1', '0'
         except Signals, error:
             self.fail("Raised %s in %s" % (error, s))