pythongh-113804: Add 'x' format to float.format()

vstinner · Jun 2, 2024 · 9f63b2a · 9f63b2a
1 parent 53b1981
commit 9f63b2a
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Showing 8 changed files with 56 additions and 3 deletions.
diff --git a/Doc/library/string.rst b/Doc/library/string.rst
@@ -571,6 +571,11 @@ The available presentation types for :class:`float` and
    |         | the current locale setting to insert the appropriate     |
    |         | number separator characters.                             |
    +---------+----------------------------------------------------------+
+   | ``'x'`` | For :class:`float`, hex format. Outputs the number in    |
+   |         | base 16, using lower-case letters for the digits above 9.|
+   |         | The alternate form adds ``'0x'`` prefix.                .|
+   |         | Precision and width are ignored.                         |
+   +---------+----------------------------------------------------------+
    | ``'%'`` | Percentage. Multiplies the number by 100 and displays    |
    |         | in fixed (``'f'``) format, followed by a percent sign.   |
    +---------+----------------------------------------------------------+

diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
@@ -75,6 +75,10 @@ New Features
 Other Language Changes
 ======================
 
+* Add ``x`` format to :meth:`float.format`: similar formatting than
+  :meth:`float.hex` without the ``'0x'`` prefix. The alternate format ``#x``
+  uses the ``'0x'`` prefix. Precision and width are ignored.
+  (Contributed by Victor Stinner in :gh:`113804`.)
 
 
 New Modules

diff --git a/Include/internal/pycore_global_objects_fini_generated.h b/Include/internal/pycore_global_objects_fini_generated.h
diff --git a/Include/internal/pycore_global_strings.h b/Include/internal/pycore_global_strings.h
@@ -46,6 +46,7 @@ struct _Py_global_strings {
         STRUCT_FOR_STR(dot_locals, ".<locals>")
         STRUCT_FOR_STR(empty, "")
         STRUCT_FOR_STR(generic_base, ".generic_base")
+        STRUCT_FOR_STR(hex, "hex")
         STRUCT_FOR_STR(json_decoder, "json.decoder")
         STRUCT_FOR_STR(kwdefaults, ".kwdefaults")
         STRUCT_FOR_STR(list_err, "list index out of range")

diff --git a/Include/internal/pycore_runtime_init_generated.h b/Include/internal/pycore_runtime_init_generated.h
diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py
@@ -700,12 +700,24 @@ def test_format(self):
         # % formatting
         self.assertEqual(format(-1.0, '%'), '-100.000000%')
 
+        # x formatting
+        for value in (-1.5, -0.0, 0.0, 1.0, 3.14):
+            with self.subTest(value=value):
+                self.assertEqual(format(value, 'x'), value.hex()[2:])
+                self.assertEqual(format(value, '#x'), value.hex())
+
+        class MyFloat(float):
+            def hex(self):
+                return 123
+
+        self.assertEqual(format(MyFloat(1.0), 'x'), (1.0).hex()[2:])
+
         # conversion to string should fail
         self.assertRaises(ValueError, format, 3.0, "s")
 
         # confirm format options expected to fail on floats, such as integer
         # presentation types
-        for format_spec in 'sbcdoxX':
+        for format_spec in 'sbcdoX':
             self.assertRaises(ValueError, format, 0.0, format_spec)
             self.assertRaises(ValueError, format, 1.0, format_spec)
             self.assertRaises(ValueError, format, -1.0, format_spec)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-06-02-17-09-37.gh-issue-113804.qmkmrK.rst b/Misc/NEWS.d/next/Core and Builtins/2024-06-02-17-09-37.gh-issue-113804.qmkmrK.rst
@@ -0,0 +1,4 @@
+Add ``x`` format to :meth:`float.format`: similar formatting than
+:meth:`float.hex` without the ``'0x'`` prefix. The alternate format ``#x``
+uses the ``'0x'`` prefix. Precision and width are ignored. Patch by Victor
+Stinner.
diff --git a/Python/formatter_unicode.c b/Python/formatter_unicode.c
@@ -1085,14 +1085,38 @@ format_float_internal(PyObject *value,
         default_precision = 0;
     }
 
-    if (type == 'n')
+    if (type == 'n') {
         /* 'n' is the same as 'g', except for the locale used to
            format the result. We take care of that later. */
         type = 'g';
+    }
+
+    if (type == 'x') {
+        _Py_DECLARE_STR(hex, "hex");
+        PyObject *hex_str = PyObject_CallMethodObjArgs(
+                                    (PyObject*)&PyFloat_Type,
+                                    &_Py_STR(hex), value, NULL);
+        if (hex_str == NULL) {
+            return -1;
+        }
+        assert(PyUnicode_Check(hex_str));
+
+        if (format->alternate) {
+            result = _PyUnicodeWriter_WriteStr(writer, hex_str);
+        }
+        else {
+            result = _PyUnicodeWriter_WriteSubstring(
+                                writer, hex_str,
+                                2, PyUnicode_GET_LENGTH(hex_str));
+        }
+        Py_DECREF(hex_str);
+        return result;
+    }
 
     val = PyFloat_AsDouble(value);
-    if (val == -1.0 && PyErr_Occurred())
+    if (val == -1.0 && PyErr_Occurred()) {
         goto done;
+    }
 
     if (type == '%') {
         type = 'f';
@@ -1573,6 +1597,7 @@ _PyFloat_FormatAdvancedWriter(_PyUnicodeWriter *writer,
     case 'g':
     case 'G':
     case 'n':
+    case 'x':
     case '%':
         /* no conversion, already a float.  do the formatting */
         return format_float_internal(obj, &format, writer);