gh-125196: Add PyUnicodeWriter_Fill() function

Doc/c-api/unicode.rst

@@ -1663,6 +1663,15 @@ object.
    On success, return ``0``.
    On error, set an exception, leave the writer unchanged, and return ``-1``.
 
+.. c:function:: int PyUnicodeWriter_Fill(PyUnicodeWriter *writer, Py_ssize_t len, Py_UCS4 ch)
+
+   Write *len* times the single Unicode character *ch* into *writer*.
+
+   *len* must not be negative.
+
+   On success, return ``0``.
+   On error, set an exception, leave the writer unchanged, and return ``-1``.
+
 .. c:function:: int PyUnicodeWriter_Format(PyUnicodeWriter *writer, const char *format, ...)
 
    Similar to :c:func:`PyUnicode_FromFormat`, but write the output directly into *writer*.

Doc/whatsnew/3.14.rst

@@ -639,6 +639,7 @@ New Features
   * :c:func:`PyUnicodeWriter_WriteStr`
   * :c:func:`PyUnicodeWriter_WriteRepr`
   * :c:func:`PyUnicodeWriter_WriteSubstring`
+  * :c:func:`PyUnicodeWriter_Fill`
   * :c:func:`PyUnicodeWriter_Format`
   * :c:func:`PyUnicodeWriter_DecodeUTF8Stateful`
 

Include/cpython/unicodeobject.h

@@ -467,6 +467,10 @@ PyAPI_FUNC(int) PyUnicodeWriter_WriteUCS4(
     PyUnicodeWriter *writer,
     Py_UCS4 *str,
     Py_ssize_t size);
+PyAPI_FUNC(int) PyUnicodeWriter_Fill(
+    PyUnicodeWriter *writer,
+    Py_ssize_t len,
+    Py_UCS4 ch);
 
 PyAPI_FUNC(int) PyUnicodeWriter_WriteStr(
     PyUnicodeWriter *writer,

Lib/test/test_capi/test_unicode.py

@@ -1744,8 +1744,11 @@ def test_basic(self):
         # test PyUnicodeWriter_WriteRepr()
         writer.write_repr("repr")
 
+        # test PyUnicodeWriter_Fill()
+        writer.fill(3, ".")
+
         self.assertEqual(writer.finish(),
-                         "var=long value 'repr'")
+                         "var=long value 'repr'...")
 
     def test_utf8(self):
         writer = self.create_writer(0)
@@ -1867,6 +1870,17 @@ def test_substring_empty(self):
         writer.write_substring("abc", 1, 1)
         self.assertEqual(writer.finish(), '')
 
+    def test_fill(self):
+        writer = self.create_writer(0)
+        writer.fill(0, "#")
+        writer.write_char('(')
+        writer.fill(3, ".")
+        writer.write_char(')')
+        writer.fill(5, "-")
+        writer.write_char('.')
+        self.assertEqual(writer.finish(),
+                         "(...)-----.")
+
 
 @unittest.skipIf(ctypes is None, 'need ctypes')
 class PyUnicodeWriterFormatTest(unittest.TestCase):

Misc/NEWS.d/next/C_API/2024-10-09-17-58-02.gh-issue-125196.azFHal.rst

@@ -0,0 +1 @@
+Add :c:func:`PyUnicodeWriter_Fill` function. Patch by Victor Stinner.

Modules/_testcapi/unicode.c

@@ -510,6 +510,27 @@ writer_finish(PyObject *self_raw, PyObject *Py_UNUSED(args))
 }
 
 
+static PyObject*
+writer_fill(PyObject *self_raw, PyObject *args)
+{
+    WriterObject *self = (WriterObject *)self_raw;
+    if (writer_check(self) < 0) {
+        return NULL;
+    }
+
+    Py_ssize_t len;
+    int ch;
+    if (!PyArg_ParseTuple(args, "nC", &len, &ch)) {
+        return NULL;
+    }
+
+    if (PyUnicodeWriter_Fill(self->writer, len, ch) < 0) {
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
+
 static PyMethodDef writer_methods[] = {
     {"write_char", _PyCFunction_CAST(writer_write_char), METH_VARARGS},
     {"write_utf8", _PyCFunction_CAST(writer_write_utf8), METH_VARARGS},
@@ -519,6 +540,7 @@ static PyMethodDef writer_methods[] = {
     {"write_repr", _PyCFunction_CAST(writer_write_repr), METH_VARARGS},
     {"write_substring", _PyCFunction_CAST(writer_write_substring), METH_VARARGS},
     {"decodeutf8stateful", _PyCFunction_CAST(writer_decodeutf8stateful), METH_VARARGS},
+    {"fill", _PyCFunction_CAST(writer_fill), METH_VARARGS},
     {"get_pointer", _PyCFunction_CAST(writer_get_pointer), METH_VARARGS},
     {"finish", _PyCFunction_CAST(writer_finish), METH_NOARGS},
     {NULL,              NULL}           /* sentinel */

Objects/unicodeobject.c

@@ -13572,6 +13572,33 @@ PyUnicodeWriter_WriteChar(PyUnicodeWriter *writer, Py_UCS4 ch)
     return _PyUnicodeWriter_WriteChar((_PyUnicodeWriter*)writer, ch);
 }
 
+int
+PyUnicodeWriter_Fill(PyUnicodeWriter *pub_writer, Py_ssize_t len, Py_UCS4 ch)
+{
+    if (len < 0) {
+        PyErr_Format(PyExc_ValueError, "len must not be negative");
+        return -1;
+    }
+    if (ch > MAX_UNICODE) {
+        PyErr_SetString(PyExc_ValueError,
+                        "character must be in range(0x110000)");
+        return -1;
+    }
+
+    if (len == 0) {
+        return 0;
+    }
+
+    _PyUnicodeWriter *writer = (_PyUnicodeWriter *)pub_writer;
+    if (_PyUnicodeWriter_Prepare(writer, len, ch) < 0) {
+        return -1;
+    }
+
+    _PyUnicode_FastFill(writer->buffer, writer->pos, len, ch);
+    writer->pos += len;
+    return 0;
+}
+
 int
 _PyUnicodeWriter_WriteStr(_PyUnicodeWriter *writer, PyObject *str)
 {