gh-129559: Add bytearray.resize()

Doc/c-api/bytearray.rst

@@ -74,6 +74,11 @@ Direct API functions
 .. c:function:: int PyByteArray_Resize(PyObject *bytearray, Py_ssize_t len)
 
  Resize the internal buffer of *bytearray* to *len*.
+ Failure is a ``-1`` return with an exception set.
+
+ .. versionchanged:: next
+ A negative *len* will now result in an exception being set and -1 returned.
+
 
 Macros
 ^^^^^^

Doc/library/stdtypes.rst

@@ -2841,6 +2841,38 @@ 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. *size* must be
+ greater than or equal to 0.
+
+ If the :class:`bytearray` needs to shrink, bytes beyond *size* are truncated.
+
+ If the :class:`bytearray` needs to grow, all new bytes, those beyond *size*,
+ will be set to null bytes.
+
+
+ This is equivalent to:
+
+ >>> def resize(ba, size):
+ ... if len(ba) > size:
+ ... del ba[size:]
+ ... else:
+ ... ba += b'\0' * (size - len(ba))
+
+ Examples:
+
+ >>> shrink = bytearray(b'abc')
+ >>> shrink.resize(1)
+ >>> (shrink, len(shrink))
+ (bytearray(b'a'), 1)
+ >>> grow = bytearray(b'abc')
+ >>> grow.resize(5)
+ >>> (grow, len(grow))
+ (bytearray(b'abc\x00\x00'), 5)
+
+ .. 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 +1359,44 @@ 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)
+ # Bytes beyond set values must be cleared.
+ self.assertEqual(ba, bytearray(b'abc\0\0\0\0\0\0\0'))
+
+ ba[3:10] = b'defghij'
+ self.assertEqual(ba, bytearray(b'abcdefghij'))
+
+ self.assertIsNone(ba.resize(2 ** 20))
+ self.assertEqual(len(ba), 2**20)
+ self.assertEqual(ba, bytearray(b'abcdefghij' + b'\0' * (2 ** 20 - 10)))
+
+ self.assertIsNone(ba.resize(0))
+ self.assertEqual(ba, bytearray())
+
+ self.assertIsNone(ba.resize(10))
+ self.assertEqual(ba, bytearray(b'\0' * 10))
+
+ # Subclass
+ ba = ByteArraySubclass(b'abcdef')
+ self.assertIsNone(ba.resize(3))
+ self.assertEqual(ba, bytearray(b'abc'))
+
+ # Check arguments
+ self.assertRaises(TypeError, bytearray().resize)
+ self.assertRaises(TypeError, bytearray().resize, (10, 10))
+
+ self.assertRaises(ValueError, bytearray().resize, -1)
+ self.assertRaises(ValueError, bytearray().resize, -200)
+ self.assertRaises(MemoryError, bytearray().resize, sys.maxsize)
+ self.assertRaises(MemoryError, bytearray(1000).resize, sys.maxsize)
+
+
  def test_setitem(self):
  def setitem_as_mapping(b, i, val):
  b[i] = val
@@ -1715,17 +1753,18 @@ def test_resize_forbidden(self):
  # if it wouldn't reallocate the underlying buffer.
  # Furthermore, no destructive changes to the buffer may be applied
  # before raising the error.
- b = bytearray(range(10))
+ b = bytearray(10)
  v = memoryview(b)
- def resize(n):
+ def manual_resize(n):
  b[1:-1] = range(n + 1, 2*n - 1)
- resize(10)
+b.resize(10)
  orig = b[:]
- self.assertRaises(BufferError, resize, 11)
+ self.assertRaises(BufferError, b.resize, 11)
+ self.assertRaises(BufferError, manual_resize, 11)
  self.assertEqual(b, orig)
- self.assertRaises(BufferError, resize, 9)
+ self.assertRaises(BufferError, b.resize, 9)
  self.assertEqual(b, orig)
- self.assertRaises(BufferError, resize, 0)
+ self.assertRaises(BufferError, b.resize, 0)
  self.assertEqual(b, orig)
  # Other operations implying resize
  self.assertRaises(BufferError, b.pop, 0)

Lib/test/test_capi/test_bytearray.py

@@ -151,10 +151,11 @@ def test_resize(self):
  self.assertEqual(resize(ba, 3), 0)
  self.assertEqual(ba, bytearray(b'abc'))
 
+ self.assertRaises(ValueError, resize, bytearray(), -1)
+ self.assertRaises(ValueError, resize, bytearray(), -200)
  self.assertRaises(MemoryError, resize, bytearray(), PY_SSIZE_T_MAX)
  self.assertRaises(MemoryError, resize, bytearray(1000), PY_SSIZE_T_MAX)
 
- # CRASHES resize(bytearray(b'abc'), -1)
  # CRASHES resize(b'abc', 0)
  # CRASHES resize(object(), 0)
  # CRASHES resize(NULL, 0)

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

@@ -0,0 +1,2 @@
+Add :meth:`bytearray.resize` method 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_ValueError,
+ "Can only resize to positive sizes, got %zd", requested_size);
+ return -1;
+ }
 
  if (requested_size == Py_SIZE(self)) {
  return 0;
@@ -1388,6 +1393,31 @@ 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]*/
+{
+ Py_ssize_t start_size = PyByteArray_GET_SIZE(self);
+ int result = PyByteArray_Resize((PyObject *)self, size);
+ if (result < 0) {
+ return NULL;
+ }
+ // Set new bytes to null bytes
+ if (size > start_size) {
+ memset(PyByteArray_AS_STRING(self) + start_size, 0, size - start_size);
+ }
+ Py_RETURN_NONE;
+}
+
+
 /*[clinic input]
 bytearray.translate
 
@@ -2361,6 +2391,7 @@ 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