mirror of https://github.com/python/cpython.git
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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@ -598,6 +598,23 @@ Decimal objects
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.. versionadded:: 3.1
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.. classmethod:: from_number(number)
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Alternative constructor that only accepts instances of
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:class:`float`, :class:`int` or :class:`Decimal`, but not strings
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or tuples.
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.. doctest::
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>>> Decimal.from_number(314)
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Decimal('314')
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>>> Decimal.from_number(0.1)
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Decimal('0.1000000000000000055511151231257827021181583404541015625')
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>>> Decimal.from_number(Decimal('3.14'))
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Decimal('3.14')
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.. versionadded:: 3.14
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.. method:: fma(other, third, context=None)
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Fused multiply-add. Return self*other+third with no rounding of the
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@ -239,6 +239,12 @@ ctypes
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to help match a non-default ABI.
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(Contributed by Petr Viktorin in :gh:`97702`.)
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decimal
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-------
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* Add alternative :class:`~decimal.Decimal` constructor
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:meth:`Decimal.from_number() <decimal.Decimal.from_number>`.
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(Contributed by Serhiy Storchaka in :gh:`121798`.)
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dis
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---
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@ -582,6 +582,21 @@ def __new__(cls, value="0", context=None):
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raise TypeError("Cannot convert %r to Decimal" % value)
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@classmethod
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def from_number(cls, number):
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"""Converts a real number to a decimal number, exactly.
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>>> Decimal.from_number(314) # int
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Decimal('314')
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>>> Decimal.from_number(0.1) # float
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Decimal('0.1000000000000000055511151231257827021181583404541015625')
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>>> Decimal.from_number(Decimal('3.14')) # another decimal instance
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Decimal('3.14')
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"""
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if isinstance(number, (int, Decimal, float)):
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return cls(number)
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raise TypeError("Cannot convert %r to Decimal" % number)
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@classmethod
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def from_float(cls, f):
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"""Converts a float to a decimal number, exactly.
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@ -812,6 +812,29 @@ def test_explicit_context_create_from_float(self):
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x = random.expovariate(0.01) * (random.random() * 2.0 - 1.0)
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self.assertEqual(x, float(nc.create_decimal(x))) # roundtrip
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def test_from_number(self, cls=None):
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Decimal = self.decimal.Decimal
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if cls is None:
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cls = Decimal
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def check(arg, expected):
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d = cls.from_number(arg)
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self.assertIs(type(d), cls)
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self.assertEqual(d, expected)
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check(314, Decimal(314))
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check(3.14, Decimal.from_float(3.14))
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check(Decimal('3.14'), Decimal('3.14'))
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self.assertRaises(TypeError, cls.from_number, 3+4j)
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self.assertRaises(TypeError, cls.from_number, '314')
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self.assertRaises(TypeError, cls.from_number, (0, (3, 1, 4), 0))
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self.assertRaises(TypeError, cls.from_number, object())
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def test_from_number_subclass(self, cls=None):
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class DecimalSubclass(self.decimal.Decimal):
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pass
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self.test_from_number(DecimalSubclass)
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def test_unicode_digits(self):
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Decimal = self.decimal.Decimal
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@ -0,0 +1,2 @@
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Add alternative :class:`~decimal.Decimal` constructor
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:meth:`Decimal.from_number() <decimal.Decimal.from_number>`.
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@ -2857,6 +2857,51 @@ dec_from_float(PyObject *type, PyObject *pyfloat)
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return result;
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}
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/* 'v' can have any numeric type accepted by the Decimal constructor. Attempt
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an exact conversion. If the result does not meet the restrictions
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for an mpd_t, fail with InvalidOperation. */
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static PyObject *
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PyDecType_FromNumberExact(PyTypeObject *type, PyObject *v, PyObject *context)
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{
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decimal_state *state = get_module_state_by_def(type);
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assert(v != NULL);
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if (PyDec_Check(state, v)) {
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return PyDecType_FromDecimalExact(type, v, context);
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}
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else if (PyLong_Check(v)) {
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return PyDecType_FromLongExact(type, v, context);
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}
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else if (PyFloat_Check(v)) {
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if (dec_addstatus(context, MPD_Float_operation)) {
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return NULL;
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}
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return PyDecType_FromFloatExact(type, v, context);
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}
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else {
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PyErr_Format(PyExc_TypeError,
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"conversion from %s to Decimal is not supported",
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Py_TYPE(v)->tp_name);
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return NULL;
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}
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}
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/* class method */
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static PyObject *
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dec_from_number(PyObject *type, PyObject *number)
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{
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PyObject *context;
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PyObject *result;
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decimal_state *state = get_module_state_by_def((PyTypeObject *)type);
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CURRENT_CONTEXT(state, context);
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result = PyDecType_FromNumberExact(state->PyDec_Type, number, context);
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if (type != (PyObject *)state->PyDec_Type && result != NULL) {
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Py_SETREF(result, PyObject_CallFunctionObjArgs(type, result, NULL));
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}
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return result;
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}
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/* create_decimal_from_float */
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static PyObject *
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ctx_from_float(PyObject *context, PyObject *v)
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@ -5052,6 +5097,7 @@ static PyMethodDef dec_methods [] =
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/* Miscellaneous */
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{ "from_float", dec_from_float, METH_O|METH_CLASS, doc_from_float },
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{ "from_number", dec_from_number, METH_O|METH_CLASS, doc_from_number },
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{ "as_tuple", PyDec_AsTuple, METH_NOARGS, doc_as_tuple },
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{ "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\
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\n\
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\n");
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PyDoc_STRVAR(doc_from_number,
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"from_number($type, number, /)\n--\n\n\
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Class method that converts a real number to a decimal number, exactly.\n\
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\n\
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>>> Decimal.from_number(314) # int\n\
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Decimal('314')\n\
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>>> Decimal.from_number(0.1) # float\n\
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Decimal('0.1000000000000000055511151231257827021181583404541015625')\n\
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>>> Decimal.from_number(Decimal('3.14')) # another decimal instance\n\
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Decimal('3.14')\n\
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\n\
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\n");
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PyDoc_STRVAR(doc_fma,
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"fma($self, /, other, third, context=None)\n--\n\n\
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Fused multiply-add. Return self*other+third with no rounding of the\n\
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