gh-129559: Add bytearray.resize()

Add `bytearray.resize()` which wraps `PyByteArray_Resize`

Author: cmaloney

Doc/library/stdtypes.rst

@@ -2841,6 +2841,13 @@ objects.
          optional *sep* and *bytes_per_sep* parameters to insert separators
          between bytes in the hex output.
 
+   .. method:: resize(size)
+
+      Resize the :class:`bytearray` to contain size bytes with a NULL byte
+      following.
+
+   .. versionadded:: next
+
 Since bytearray objects are sequences of integers (akin to a list), for a
 bytearray object *b*, ``b[0]`` will be an integer, while ``b[0:1]`` will be
 a bytearray object of length 1.  (This contrasts with text strings, where

Lib/test/test_bytes.py

@@ -1359,6 +1359,33 @@ def by(s):
         b = by("Hello, world")
         self.assertEqual(re.findall(br"\w+", b), [by("Hello"), by("world")])
 
+    def test_resize(self):
+        ba = bytearray(b'abcdef')
+        self.assertIsNone(ba.resize(3))
+        self.assertEqual(ba, bytearray(b'abc'))
+        self.assertIsNone(ba.resize(10))
+        self.assertEqual(len(ba), 10)
+        self.assertEqual(ba[:3], bytearray(b'abc'))
+        self.assertIsNone(ba.resize(2**20))
+        self.assertEqual(len(ba), 2**20)
+        self.assertEqual(ba[:3], bytearray(b'abc'))
+        self.assertIsNone(ba.resize(0))
+        self.assertEqual(ba, bytearray())
+
+        ba = ByteArraySubclass(b'abcdef')
+        self.assertIsNone(ba.resize(3))
+        self.assertEqual(ba, bytearray(b'abc'))
+
+        # Check arguments
+        self.assertRaises(TypeError, lambda: bytearray().resize())
+        self.assertRaises(TypeError, lambda: bytearray().resize(10, 10))
+
+        self.assertRaises(BufferError, lambda: bytearray().resize(-1))
+        self.assertRaises(BufferError, lambda: bytearray().resize(-200))
+        self.assertRaises(MemoryError, lambda: bytearray().resize(sys.maxsize))
+        self.assertRaises(MemoryError, lambda: bytearray(1000).resize(sys.maxsize))
+
+
     def test_setitem(self):
         def setitem_as_mapping(b, i, val):
             b[i] = val

Misc/NEWS.d/next/Library/2025-02-01-14-55-33.gh-issue-129559.hQCeAz.rst

@@ -0,0 +1,3 @@
+Add :meth:`bytearray.resize` method to :class:`bytearray` wrapping
+:c:func:`PyByteArray_Resize` so :class:`bytearray` can be efficiently
+resized in place.

Objects/bytearrayobject.c

@@ -184,7 +184,12 @@ PyByteArray_Resize(PyObject *self, Py_ssize_t requested_size)
     assert(self != NULL);
     assert(PyByteArray_Check(self));
     assert(logical_offset <= alloc);
-    assert(requested_size >= 0);
+
+    if (requested_size < 0) {
+        PyErr_Format(PyExc_BufferError,
+            "Can only resize to positive sizes, got %zd.", requested_size);
+        return -1;
+    }
 
     if (requested_size == Py_SIZE(self)) {
         return 0;
@@ -1388,6 +1393,26 @@ bytearray_removesuffix_impl(PyByteArrayObject *self, Py_buffer *suffix)
 }
 
 
+/*[clinic input]
+bytearray.resize
+    size: Py_ssize_t
+        New size to resize to..
+    /
+Resize the internal buffer of bytearray to len.
+[clinic start generated code]*/
+
+static PyObject *
+bytearray_resize_impl(PyByteArrayObject *self, Py_ssize_t size)
+/*[clinic end generated code: output=f73524922990b2d9 input=75fd4d17c4aa47d3]*/
+{
+    int result = PyByteArray_Resize((PyObject *)self, size);
+    if (result == -1) {
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
+
 /*[clinic input]
 bytearray.translate
 
@@ -2361,6 +2386,7 @@ static PyMethodDef bytearray_methods[] = {
     BYTEARRAY_REPLACE_METHODDEF
     BYTEARRAY_REMOVEPREFIX_METHODDEF
     BYTEARRAY_REMOVESUFFIX_METHODDEF
+    BYTEARRAY_RESIZE_METHODDEF
     BYTEARRAY_REVERSE_METHODDEF
     BYTEARRAY_RFIND_METHODDEF
     BYTEARRAY_RINDEX_METHODDEF