gh-121798: Add class method Decimal.from_number() (GH-121801)

It is an alternate constructor which only accepts a single numeric argument.
Unlike to Decimal.from_float() it accepts also Decimal.
Unlike to the standard constructor, it does not accept strings and tuples.
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Serhiy Storchaka 2024-10-14 11:24:01 +03:00 committed by GitHub
parent 4b358ee647
commit 5217328f93
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7 changed files with 122 additions and 0 deletions

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@ -598,6 +598,23 @@ Decimal objects
.. versionadded:: 3.1
.. classmethod:: from_number(number)
Alternative constructor that only accepts instances of
:class:`float`, :class:`int` or :class:`Decimal`, but not strings
or tuples.
.. doctest::
>>> Decimal.from_number(314)
Decimal('314')
>>> Decimal.from_number(0.1)
Decimal('0.1000000000000000055511151231257827021181583404541015625')
>>> Decimal.from_number(Decimal('3.14'))
Decimal('3.14')
.. versionadded:: 3.14
.. method:: fma(other, third, context=None)
Fused multiply-add. Return self*other+third with no rounding of the

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@ -239,6 +239,12 @@ ctypes
to help match a non-default ABI.
(Contributed by Petr Viktorin in :gh:`97702`.)
decimal
-------
* Add alternative :class:`~decimal.Decimal` constructor
:meth:`Decimal.from_number() <decimal.Decimal.from_number>`.
(Contributed by Serhiy Storchaka in :gh:`121798`.)
dis
---

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@ -582,6 +582,21 @@ def __new__(cls, value="0", context=None):
raise TypeError("Cannot convert %r to Decimal" % value)
@classmethod
def from_number(cls, number):
"""Converts a real number to a decimal number, exactly.
>>> Decimal.from_number(314) # int
Decimal('314')
>>> Decimal.from_number(0.1) # float
Decimal('0.1000000000000000055511151231257827021181583404541015625')
>>> Decimal.from_number(Decimal('3.14')) # another decimal instance
Decimal('3.14')
"""
if isinstance(number, (int, Decimal, float)):
return cls(number)
raise TypeError("Cannot convert %r to Decimal" % number)
@classmethod
def from_float(cls, f):
"""Converts a float to a decimal number, exactly.

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@ -812,6 +812,29 @@ def test_explicit_context_create_from_float(self):
x = random.expovariate(0.01) * (random.random() * 2.0 - 1.0)
self.assertEqual(x, float(nc.create_decimal(x))) # roundtrip
def test_from_number(self, cls=None):
Decimal = self.decimal.Decimal
if cls is None:
cls = Decimal
def check(arg, expected):
d = cls.from_number(arg)
self.assertIs(type(d), cls)
self.assertEqual(d, expected)
check(314, Decimal(314))
check(3.14, Decimal.from_float(3.14))
check(Decimal('3.14'), Decimal('3.14'))
self.assertRaises(TypeError, cls.from_number, 3+4j)
self.assertRaises(TypeError, cls.from_number, '314')
self.assertRaises(TypeError, cls.from_number, (0, (3, 1, 4), 0))
self.assertRaises(TypeError, cls.from_number, object())
def test_from_number_subclass(self, cls=None):
class DecimalSubclass(self.decimal.Decimal):
pass
self.test_from_number(DecimalSubclass)
def test_unicode_digits(self):
Decimal = self.decimal.Decimal

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@ -0,0 +1,2 @@
Add alternative :class:`~decimal.Decimal` constructor
:meth:`Decimal.from_number() <decimal.Decimal.from_number>`.

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@ -2857,6 +2857,51 @@ dec_from_float(PyObject *type, PyObject *pyfloat)
return result;
}
/* 'v' can have any numeric type accepted by the Decimal constructor. Attempt
an exact conversion. If the result does not meet the restrictions
for an mpd_t, fail with InvalidOperation. */
static PyObject *
PyDecType_FromNumberExact(PyTypeObject *type, PyObject *v, PyObject *context)
{
decimal_state *state = get_module_state_by_def(type);
assert(v != NULL);
if (PyDec_Check(state, v)) {
return PyDecType_FromDecimalExact(type, v, context);
}
else if (PyLong_Check(v)) {
return PyDecType_FromLongExact(type, v, context);
}
else if (PyFloat_Check(v)) {
if (dec_addstatus(context, MPD_Float_operation)) {
return NULL;
}
return PyDecType_FromFloatExact(type, v, context);
}
else {
PyErr_Format(PyExc_TypeError,
"conversion from %s to Decimal is not supported",
Py_TYPE(v)->tp_name);
return NULL;
}
}
/* class method */
static PyObject *
dec_from_number(PyObject *type, PyObject *number)
{
PyObject *context;
PyObject *result;
decimal_state *state = get_module_state_by_def((PyTypeObject *)type);
CURRENT_CONTEXT(state, context);
result = PyDecType_FromNumberExact(state->PyDec_Type, number, context);
if (type != (PyObject *)state->PyDec_Type && result != NULL) {
Py_SETREF(result, PyObject_CallFunctionObjArgs(type, result, NULL));
}
return result;
}
/* create_decimal_from_float */
static PyObject *
ctx_from_float(PyObject *context, PyObject *v)
@ -5052,6 +5097,7 @@ static PyMethodDef dec_methods [] =
/* Miscellaneous */
{ "from_float", dec_from_float, METH_O|METH_CLASS, doc_from_float },
{ "from_number", dec_from_number, METH_O|METH_CLASS, doc_from_number },
{ "as_tuple", PyDec_AsTuple, METH_NOARGS, doc_as_tuple },
{ "as_integer_ratio", dec_as_integer_ratio, METH_NOARGS, doc_as_integer_ratio },

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@ -189,6 +189,19 @@ Decimal.from_float(0.1) is not the same as Decimal('0.1').\n\
\n\
\n");
PyDoc_STRVAR(doc_from_number,
"from_number($type, number, /)\n--\n\n\
Class method that converts a real number to a decimal number, exactly.\n\
\n\
>>> Decimal.from_number(314) # int\n\
Decimal('314')\n\
>>> Decimal.from_number(0.1) # float\n\
Decimal('0.1000000000000000055511151231257827021181583404541015625')\n\
>>> Decimal.from_number(Decimal('3.14')) # another decimal instance\n\
Decimal('3.14')\n\
\n\
\n");
PyDoc_STRVAR(doc_fma,
"fma($self, /, other, third, context=None)\n--\n\n\
Fused multiply-add. Return self*other+third with no rounding of the\n\