Issue #5835: Deprecate PyOS_ascii_formatd.
diff --git a/Doc/c-api/conversion.rst b/Doc/c-api/conversion.rst
index 1c19879..a2e2542 100644
--- a/Doc/c-api/conversion.rst
+++ b/Doc/c-api/conversion.rst
@@ -73,6 +73,43 @@
The return value is a pointer to *buffer* with the converted string or NULL if
the conversion failed.
+ .. deprecated:: 3.1
+ Use :cfunc:`PyOS_double_to_string` instead.
+
+
+.. cfunction:: char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype)
+
+ Convert a :ctype:`double` *val* to a string using supplied
+ *format_code*, *precision*, and *flags*.
+
+ *format_code* must be one of ``'e'``, ``'E'``, ``'f'``, ``'F'``, ``'g'``,
+ ``'G'``, ``'s'``, or ``'r'``. For ``'s'`` and ``'r'``, the supplied
+ *precision* must be 0 and is ignored. These specify the standard
+ :func:`str` and :func:`repr` formats, respectively.
+
+ *flags* can be zero or more of the values *Py_DTSF_SIGN*,
+ *Py_DTSF_ADD_DOT_0*, or *Py_DTSF_ALT*, or-ed together:
+
+ * *Py_DTSF_SIGN* means to always precede the returned string with a sign
+ character, even if *val* is non-negative.
+
+ * *Py_DTSF_ADD_DOT_0* means to ensure that the returned string will not look
+ like an integer.
+
+ * *Py_DTSF_ALT* means to apply "alternate" formatting rules. See the
+ documentation for the :cfunc:`PyOS_snprintf` ``'#'`` specifier for
+ details.
+
+ If *ptype* is non-NULL, then the value it points to will be set to one of
+ *Py_DTST_FINITE*, *Py_DTST_INFINITE*, or *Py_DTST_NAN*, signifying that
+ *val* is a finite number, an infinite number, or not a number, respectively.
+
+ The return value is a pointer to *buffer* with the converted string or
+ *NULL* if the conversion failed. The caller is responsible for freeing the
+ returned string by calling :cfunc:`PyMem_Free`.
+
+ .. versionadded:: 3.1
+
.. cfunction:: double PyOS_ascii_atof(const char *nptr)