python · serhiy-storchaka · Jul 15, 2024 · Jun 21, 2021 · Jun 21, 2021 · Sep 4, 2022
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
@@ -387,6 +387,8 @@ are always available.  They are listed here in alphabetical order.
    to :meth:`~object.__float__`.  If :meth:`!__float__` is not defined then it falls back
    to :meth:`~object.__index__`.
 
+   See also :meth:`complex.from_number` which only accept single numeric argument.
+
    .. note::
 
       When converting from a string, the string must not contain whitespace
@@ -684,6 +686,8 @@ are always available.  They are listed here in alphabetical order.
    ``x.__float__()``.  If :meth:`~object.__float__` is not defined then it falls back
    to :meth:`~object.__index__`.
 
+   See also :meth:`float.from_number` which only accept numeric argument.
+
    If no argument is given, ``0.0`` is returned.
 
    Examples::

diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
@@ -624,6 +624,23 @@ Additional Methods on Float
 The float type implements the :class:`numbers.Real` :term:`abstract base
 class`. float also has the following additional methods.
 
+.. classmethod:: float.from_number(x)
+
+   Class method to return a floating point number constructed from a number *x*.
+
+   If the argument is an integer or a floating point number, a
+   floating point number with the same value (within Python's floating point
+   precision) is returned.  If the argument is outside the range of a Python
+   float, an :exc:`OverflowError` will be raised.
+
+   For a general Python object ``x``, ``float.from_number(x)`` delegates to
+   ``x.__float__()``.
+   If :meth:`~object.__float__` is not defined then it falls back
+   to :meth:`~object.__index__`.
+
+   .. versionadded:: 3.13
+
+
 .. method:: float.as_integer_ratio()
 
    Return a pair of integers whose ratio is exactly equal to the
@@ -702,6 +719,25 @@ hexadecimal string representing the same number::
    '0x1.d380000000000p+11'
 
 
+Additional Methods on Complex
+-----------------------------
+
+The :class:`!complex` type implements the :class:`numbers.Complex`
+:term:`abstract base class`.
+:class:`!complex` also has the following additional methods.
+
+.. classmethod:: complex.from_number(x)
+
+   Class method to convert a number to a complex number.
+
+   For a general Python object ``x``, ``complex.from_number(x)`` delegates to
+   ``x.__complex__()``.  If :meth:`~object.__complex__` is not defined then it falls back
+   to :meth:`~object.__float__`.  If :meth:`!__float__` is not defined then it falls back
+   to :meth:`~object.__index__`.
+
+   .. versionadded:: 3.13
+
+
 .. _numeric-hash:
 
 Hashing of numeric types

diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst
@@ -75,6 +75,11 @@ New Features
 Other Language Changes
 ======================
 
+* Added class methods :meth:`float.from_number` and :meth:`complex.from_number`
+  to convert a number to :class:`float` or :class:`complex` type correspondingly.
+  They raise error if the argument is a string.
+  (Contributed by Serhiy Storchaka in :gh:`84978`.)
+
 * Allow the *count* argument of :meth:`str.replace` to be a keyword.
   (Contributed by Hugo van Kemenade in :gh:`106487`.)
 

diff --git a/Lib/test/test_complex.py b/Lib/test/test_complex.py
@@ -10,6 +10,42 @@
 
 INF = float("inf")
 NAN = float("nan")
+
+class ComplexSubclass(complex):
+    pass
+
+class OtherComplexSubclass(complex):
+    pass
+
+class MyIndex:
+    def __init__(self, value):
+        self.value = value
+
+    def __index__(self):
+        return self.value
+
+class MyInt:
+    def __init__(self, value):
+        self.value = value
+
+    def __int__(self):
+        return self.value
+
+class FloatLike:
+    def __init__(self, value):
+        self.value = value
+
+    def __float__(self):
+        return self.value
+
+class ComplexLike:
+    def __init__(self, value):
+        self.value = value
+
+    def __complex__(self):
+        return self.value
+
+
 # These tests ensure that complex math does the right thing
 
 ZERO_DIVISION = (
@@ -306,14 +342,11 @@ def test_conjugate(self):
         self.assertClose(complex(5.3, 9.8).conjugate(), 5.3-9.8j)
 
     def test_constructor(self):
-        class NS:
-            def __init__(self, value): self.value = value
-            def __complex__(self): return self.value
-        self.assertEqual(complex(NS(1+10j)), 1+10j)
-        self.assertRaises(TypeError, complex, NS(None))
+        self.assertEqual(complex(ComplexLike(1+10j)), 1+10j)
+        self.assertRaises(TypeError, complex, ComplexLike(None))
         self.assertRaises(TypeError, complex, {})
-        self.assertRaises(TypeError, complex, NS(1.5))
-        self.assertRaises(TypeError, complex, NS(1))
+        self.assertRaises(TypeError, complex, ComplexLike(1.5))
+        self.assertRaises(TypeError, complex, ComplexLike(1))
 
         self.assertAlmostEqual(complex("1+10j"), 1+10j)
         self.assertAlmostEqual(complex(10), 10+0j)
@@ -360,8 +393,7 @@ def __complex__(self): return self.value
         self.assertAlmostEqual(complex('-1e-500j'), 0.0 - 0.0j)
         self.assertAlmostEqual(complex('-1e-500+1e-500j'), -0.0 + 0.0j)
 
-        class complex2(complex): pass
-        self.assertAlmostEqual(complex(complex2(1+1j)), 1+1j)
+        self.assertAlmostEqual(complex(ComplexSubclass(1+1j)), 1+1j)
         self.assertAlmostEqual(complex(real=17, imag=23), 17+23j)
         self.assertAlmostEqual(complex(real=17+23j), 17+23j)
         self.assertAlmostEqual(complex(real=17+23j, imag=23), 17+46j)
@@ -443,33 +475,17 @@ def __complex__(self):
 
         self.assertRaises(EvilExc, complex, evilcomplex())
 
-        class float2:
-            def __init__(self, value):
-                self.value = value
-            def __float__(self):
-                return self.value
-
-        self.assertAlmostEqual(complex(float2(42.)), 42)
-        self.assertAlmostEqual(complex(real=float2(17.), imag=float2(23.)), 17+23j)
-        self.assertRaises(TypeError, complex, float2(None))
-
-        class MyIndex:
-            def __init__(self, value):
-                self.value = value
-            def __index__(self):
-                return self.value
+        self.assertAlmostEqual(complex(FloatLike(42.)), 42)
+        self.assertAlmostEqual(complex(real=FloatLike(17.), imag=FloatLike(23.)), 17+23j)
+        self.assertRaises(TypeError, complex, FloatLike(None))
 
         self.assertAlmostEqual(complex(MyIndex(42)), 42.0+0.0j)
         self.assertAlmostEqual(complex(123, MyIndex(42)), 123.0+42.0j)
         self.assertRaises(OverflowError, complex, MyIndex(2**2000))
         self.assertRaises(OverflowError, complex, 123, MyIndex(2**2000))
 
-        class MyInt:
-            def __int__(self):
-                return 42
-
-        self.assertRaises(TypeError, complex, MyInt())
-        self.assertRaises(TypeError, complex, 123, MyInt())
+        self.assertRaises(TypeError, complex, MyInt(42))
+        self.assertRaises(TypeError, complex, 123, MyInt(42))
 
         class complex0(complex):
             """Test usage of __complex__() when inheriting from 'complex'"""
@@ -508,24 +524,22 @@ class complex_subclass(complex):
 
     @support.requires_IEEE_754
     def test_constructor_special_numbers(self):
-        class complex2(complex):
-            pass
         for x in 0.0, -0.0, INF, -INF, NAN:
             for y in 0.0, -0.0, INF, -INF, NAN:
                 with self.subTest(x=x, y=y):
                     z = complex(x, y)
                     self.assertFloatsAreIdentical(z.real, x)
                     self.assertFloatsAreIdentical(z.imag, y)
-                    z = complex2(x, y)
-                    self.assertIs(type(z), complex2)
+                    z = ComplexSubclass(x, y)
+                    self.assertIs(type(z), ComplexSubclass)
                     self.assertFloatsAreIdentical(z.real, x)
                     self.assertFloatsAreIdentical(z.imag, y)
-                    z = complex(complex2(x, y))
+                    z = complex(ComplexSubclass(x, y))
                     self.assertIs(type(z), complex)
                     self.assertFloatsAreIdentical(z.real, x)
                     self.assertFloatsAreIdentical(z.imag, y)
-                    z = complex2(complex(x, y))
-                    self.assertIs(type(z), complex2)
+                    z = ComplexSubclass(complex(x, y))
+                    self.assertIs(type(z), ComplexSubclass)
                     self.assertFloatsAreIdentical(z.real, x)
                     self.assertFloatsAreIdentical(z.imag, y)
 
@@ -547,6 +561,35 @@ def test_underscores(self):
             if not any(ch in lit for ch in 'xXoObB'):
                 self.assertRaises(ValueError, complex, lit)
 
+    def test_from_number(self, cls=complex):
+        def eq(actual, expected):
+            self.assertEqual(actual, expected)
+            self.assertIs(type(actual), cls)
+
+        eq(cls.from_number(3.14), 3.14+0j)
+        eq(cls.from_number(3.14j), 3.14j)
+        eq(cls.from_number(314), 314.0+0j)
+        eq(cls.from_number(OtherComplexSubclass(3.14, 2.72)), 3.14+2.72j)
+        eq(cls.from_number(ComplexLike(3.14+2.72j)), 3.14+2.72j)
+        eq(cls.from_number(FloatLike(3.14)), 3.14+0j)
+        eq(cls.from_number(MyIndex(314)), 314.0+0j)
+
+        cNAN = complex(NAN, NAN)
+        x = cls.from_number(cNAN)
+        self.assertTrue(x != x)
+        self.assertIs(type(x), cls)
+        if cls is complex:
+            self.assertIs(cls.from_number(cNAN), cNAN)
+
+        self.assertRaises(TypeError, cls.from_number, '3.14')
+        self.assertRaises(TypeError, cls.from_number, b'3.14')
+        self.assertRaises(TypeError, cls.from_number, MyInt(314))
+        self.assertRaises(TypeError, cls.from_number, {})
+        self.assertRaises(TypeError, cls.from_number)
+
+    def test_from_number_subclass(self):
+        self.test_from_number(ComplexSubclass)
+
     def test_hash(self):
         for x in range(-30, 30):
             self.assertEqual(hash(x), hash(complex(x, 0)))

diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py
@@ -33,6 +33,28 @@ class FloatSubclass(float):
 class OtherFloatSubclass(float):
     pass
 
+class MyIndex:
+    def __init__(self, value):
+        self.value = value
+
+    def __index__(self):
+        return self.value
+
+class MyInt:
+    def __init__(self, value):
+        self.value = value
+
+    def __int__(self):
+        return self.value
+
+class FloatLike:
+    def __init__(self, value):
+        self.value = value
+
+    def __float__(self):
+        return self.value
+
+
 class GeneralFloatCases(unittest.TestCase):
 
     def test_float(self):
@@ -182,10 +204,6 @@ def test_float_with_comma(self):
 
     def test_floatconversion(self):
         # Make sure that calls to __float__() work properly
-        class Foo1(object):
-            def __float__(self):
-                return 42.
-
         class Foo2(float):
             def __float__(self):
                 return 42.
@@ -207,45 +225,29 @@ class FooStr(str):
             def __float__(self):
                 return float(str(self)) + 1
 
-        self.assertEqual(float(Foo1()), 42.)
+        self.assertEqual(float(FloatLike(42.)), 42.)
         self.assertEqual(float(Foo2()), 42.)
         with self.assertWarns(DeprecationWarning):
             self.assertEqual(float(Foo3(21)), 42.)
         self.assertRaises(TypeError, float, Foo4(42))
         self.assertEqual(float(FooStr('8')), 9.)
 
-        class Foo5:
-            def __float__(self):
-                return ""
-        self.assertRaises(TypeError, time.sleep, Foo5())
+        self.assertRaises(TypeError, time.sleep, FloatLike(""))
 
         # Issue #24731
-        class F:
-            def __float__(self):
-                return OtherFloatSubclass(42.)
+        f = FloatLike(OtherFloatSubclass(42.))
         with self.assertWarns(DeprecationWarning):
-            self.assertEqual(float(F()), 42.)
+            self.assertEqual(float(f), 42.)
         with self.assertWarns(DeprecationWarning):
-            self.assertIs(type(float(F())), float)
+            self.assertIs(type(float(f)), float)
         with self.assertWarns(DeprecationWarning):
-            self.assertEqual(FloatSubclass(F()), 42.)
+            self.assertEqual(FloatSubclass(f), 42.)
         with self.assertWarns(DeprecationWarning):
-            self.assertIs(type(FloatSubclass(F())), FloatSubclass)
-
-        class MyIndex:
-            def __init__(self, value):
-                self.value = value
-            def __index__(self):
-                return self.value
+            self.assertIs(type(FloatSubclass(f)), FloatSubclass)
 
         self.assertEqual(float(MyIndex(42)), 42.0)
         self.assertRaises(OverflowError, float, MyIndex(2**2000))
-
-        class MyInt:
-            def __int__(self):
-                return 42
-
-        self.assertRaises(TypeError, float, MyInt())
+        self.assertRaises(TypeError, float, MyInt(42))
 
     def test_keyword_args(self):
         with self.assertRaisesRegex(TypeError, 'keyword argument'):
@@ -278,6 +280,37 @@ def __new__(cls, arg, newarg=None):
         self.assertEqual(float(u), 2.5)
         self.assertEqual(u.newarg, 3)
 
+    def assertEqualAndType(self, actual, expected_value, expected_type):
+        self.assertEqual(actual, expected_value)
+        self.assertIs(type(actual), expected_type)
+
+    def test_from_number(self, cls=float):
+        def eq(actual, expected):
+            self.assertEqual(actual, expected)
+            self.assertIs(type(actual), cls)
+
+        eq(cls.from_number(3.14), 3.14)
+        eq(cls.from_number(314), 314.0)
+        eq(cls.from_number(OtherFloatSubclass(3.14)), 3.14)
+        eq(cls.from_number(FloatLike(3.14)), 3.14)
+        eq(cls.from_number(MyIndex(314)), 314.0)
+
+        x = cls.from_number(NAN)
+        self.assertTrue(x != x)
+        self.assertIs(type(x), cls)
+        if cls is float:
+            self.assertIs(cls.from_number(NAN), NAN)
+
+        self.assertRaises(TypeError, cls.from_number, '3.14')
+        self.assertRaises(TypeError, cls.from_number, b'3.14')
+        self.assertRaises(TypeError, cls.from_number, 3.14j)
+        self.assertRaises(TypeError, cls.from_number, MyInt(314))
+        self.assertRaises(TypeError, cls.from_number, {})
+        self.assertRaises(TypeError, cls.from_number)
+
+    def test_from_number_subclass(self):
+        self.test_from_number(FloatSubclass)
+
     def test_is_integer(self):
         self.assertFalse((1.1).is_integer())
         self.assertTrue((1.).is_integer())

diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-10-14-23-05-40.gh-issue-84978.Z0t6dg.rst b/Misc/NEWS.d/next/Core and Builtins/2023-10-14-23-05-40.gh-issue-84978.Z0t6dg.rst
@@ -0,0 +1 @@
+Add class methods :meth:`float.from_number` and :meth:`complex.from_number`.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Add class methods :meth:`float.from_number` and :meth:`complex.from_number`.