gh-129559: Add bytearray.resize()

Doc/c-api/bytearray.rst

@@ -73,7 +73,11 @@ Direct API functions
 
 .. c:function:: int PyByteArray_Resize(PyObject *bytearray, Py_ssize_t len)
 
-   Resize the internal buffer of *bytearray* to *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 a failure.
+
 
 Macros
 ^^^^^^

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.
+      If :class:`bytearray` needs to grow, all new bytes will be set to null bytes.
+
+      .. 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 +1359,38 @@ 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))
+
+        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, 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

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(BufferError, resize, bytearray(), -1)
+        self.assertRaises(BufferError, 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 +1,3 @@
+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_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 provide consistent / safer behavior in Python version.
+    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