[Python-checkins] r64438 - in python/trunk: Lib/test/test_builtin.py Misc/NEWS Objects/floatobject.c

[Eric Smith]

What's the plan on implementing this in 3.0?  3.0 doesn't have __bin__, 
__oct__, and __hex__.  The bin(), oct(), and hex() machinery there uses 
PyNumber_ToBase(), which uses PyNumber_Index(), which uses __index__. 
Obviously we don't want float to grow a __index__.

If you really must add this feature,  I suggest that the implementation 
in 2.6 and 3.0 both modify PyNumber_ToBase() to explicitly check for 
float.  In 3.0, there's no way to hook this for other types, anyway 
(short of implementing __index__, but that has other effects).

Eric.

raymond.hettinger wrote:
> Author: raymond.hettinger
> Date: Sat Jun 21 08:39:53 2008
> New Revision: 64438
> 
> Log:
> Issue 3008: hex/oct/bin can show floats exactly.
> 
> Modified:
>    python/trunk/Lib/test/test_builtin.py
>    python/trunk/Misc/NEWS
>    python/trunk/Objects/floatobject.c
> 
> Modified: python/trunk/Lib/test/test_builtin.py
> ==============================================================================
> --- python/trunk/Lib/test/test_builtin.py	(original)
> +++ python/trunk/Lib/test/test_builtin.py	Sat Jun 21 08:39:53 2008
> @@ -631,6 +631,15 @@
>          self.assertEqual(hex(-16), '-0x10')
>          self.assertEqual(hex(-16L), '-0x10L')
>          self.assertRaises(TypeError, hex, {})
> +        self.assertEqual(hex(3.125), '0x19 * 2.0 ** -3')
> +        self.assertEqual(hex(0.0), '0x0 * 2.0 ** 0')
> +        for sv in float('nan'), float('inf'), float('-inf'):
> +            self.assertEqual(hex(sv), repr(sv))
> +        for i in range(100):
> +            x = random.expovariate(.05)
> +            self.assertEqual(eval(hex(x)), x, (x, hex(x), eval(hex(x))))
> +            self.assertEqual(eval(hex(-x)), -x)
> +            self.assertEqual(hex(-x), ('-' + hex(x)))
>  
>      def test_id(self):
>          id(None)
> @@ -914,6 +923,15 @@
>          self.assertEqual(oct(-100), '-0144')
>          self.assertEqual(oct(-100L), '-0144L')
>          self.assertRaises(TypeError, oct, ())
> +        self.assertEqual(oct(3.125), '031 * 2.0 ** -3')
> +        self.assertEqual(oct(0.0), '0 * 2.0 ** 0')
> +        for sv in float('nan'), float('inf'), float('-inf'):
> +            self.assertEqual(oct(sv), repr(sv))
> +        for i in range(100):
> +            x = random.expovariate(.05)
> +            self.assertEqual(eval(oct(x)), x)
> +            self.assertEqual(eval(oct(-x)), -x)
> +            self.assertEqual(oct(-x), ('-' + oct(x)))
>  
>      def write_testfile(self):
>          # NB the first 4 lines are also used to test input and raw_input, below
> @@ -1466,6 +1484,15 @@
>          self.assertEqual(bin(2**65-1), '0b' + '1' * 65)
>          self.assertEqual(bin(-(2**65)), '-0b1' + '0' * 65)
>          self.assertEqual(bin(-(2**65-1)), '-0b' + '1' * 65)
> +        self.assertEqual(bin(3.125), '0b11001 * 2.0 ** -3')
> +        self.assertEqual(bin(0.0), '0b0 * 2.0 ** 0')
> +        for sv in float('nan'), float('inf'), float('-inf'):
> +            self.assertEqual(bin(sv), repr(sv))
> +        for i in range(100):
> +            x = random.expovariate(.05)
> +            self.assertEqual(eval(bin(x)), x)
> +            self.assertEqual(eval(bin(-x)), -x)
> +            self.assertEqual(bin(-x), ('-' + bin(x)))
>  
>  class TestSorted(unittest.TestCase):
>  
> 
> Modified: python/trunk/Misc/NEWS
> ==============================================================================
> --- python/trunk/Misc/NEWS	(original)
> +++ python/trunk/Misc/NEWS	Sat Jun 21 08:39:53 2008
> @@ -17,6 +17,9 @@
>    slice(None, 10, -1).indices(10) returns (9, 9, -1) instead of (9,
>    10, -1).
>  
> +- Issue 3008: hex(), oct(), and bin() can now create exact reprs 
> +  for floats.
> +
>  - Make bin() implementation parallel oct() and hex().
>  
>  
> 
> Modified: python/trunk/Objects/floatobject.c
> ==============================================================================
> --- python/trunk/Objects/floatobject.c	(original)
> +++ python/trunk/Objects/floatobject.c	Sat Jun 21 08:39:53 2008
> @@ -1204,6 +1204,62 @@
>  ">>> (-.25).as_integer_ratio()\n"
>  "(-1, 4)");
>  
> +static PyObject *
> +_float_to_base(PyFloatObject *v, unaryfunc int_to_base)
> +{
> +	PyObject *mant, *conv, *result;
> +	double x, fr;
> +	int i, exp, n;
> +	char *conv_str;
> +
> +	CONVERT_TO_DOUBLE(((PyObject *)v), x);
> +	if (!Py_IS_FINITE(x))
> +		return PyObject_Repr((PyObject *)v);
> +	fr = frexp(x, &exp);
> +	for (i=0; i<300 && fr != floor(fr) ; i++) {
> +		fr *= 2.0;
> +		exp--;
> +	}
> +	mant = PyLong_FromDouble(floor(fr));
> +	if (mant == NULL)
> +		return NULL;
> +	conv = int_to_base(mant);
> +	Py_DECREF(mant);
> +	if (conv== NULL)
> +		return NULL;
> +	n = PyString_GET_SIZE(conv);
> +	conv_str = PyString_AS_STRING(conv);
> +	/* Remove the trailing 'L' if present */
> +	if (n && conv_str[n-1] == 'L') {
> +		PyObject *newconv = PySequence_GetSlice(conv, 0, -1);
> +		Py_DECREF(conv);
> +		if (newconv == NULL)
> +			return NULL;
> +		conv = newconv;
> +		conv_str = PyString_AS_STRING(conv);
> +	}
> +	result = PyString_FromFormat("%s * 2.0 ** %d", conv_str, exp);
> +	Py_DECREF(conv);
> +	return result;
> +}
> +
> +static PyObject *
> +float_hex(PyFloatObject *v)
> +{
> +	return _float_to_base(v, PyLong_Type.tp_as_number->nb_hex);
> +}
> +
> +static PyObject *
> +float_oct(PyFloatObject *v)
> +{
> +	return _float_to_base(v, PyLong_Type.tp_as_number->nb_oct);
> +}
> +
> +static PyObject *
> +float_bin(PyFloatObject *v)
> +{
> +	return _float_to_base(v, PyLong_Type.tp_as_number->nb_bin);
> +}
>  
>  static PyObject *
>  float_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
> @@ -1490,8 +1546,8 @@
>  	float_trunc, 	/*nb_int*/
>  	float_trunc, 	/*nb_long*/
>  	float_float,	/*nb_float*/
> -	0,		/* nb_oct */
> -	0,		/* nb_hex */
> +	(unaryfunc)float_oct,		/* nb_oct */
> +	(unaryfunc)float_hex,		/* nb_hex */
>  	0,		/* nb_inplace_add */
>  	0,		/* nb_inplace_subtract */
>  	0,		/* nb_inplace_multiply */
> @@ -1507,6 +1563,8 @@
>  	float_div,	/* nb_true_divide */
>  	0,		/* nb_inplace_floor_divide */
>  	0,		/* nb_inplace_true_divide */
> +	0,		/* nb_index */
> +	(unaryfunc)float_bin,		/* nb_bin */
>  };
>  
>  PyTypeObject PyFloat_Type = {
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