Objects/memoryobject.c

Source:

cpython 3.14 @ ab2d84fe1023/Objects/memoryobject.c ↗

memoryview exposes the buffer protocol as a Python object. It allows zero-copy access to the underlying memory of bytes, bytearray, array.array, and any object implementing tp_as_buffer.

Map

Lines	Symbol	Role
1-200	PyMemoryViewObject, Py_buffer	Object layout and buffer info struct
201-500	memoryview_new, PyMemoryView_FromObject	Creation
501-800	memory_getitem, memory_setitem	Indexed access with format unpacking
801-1100	memory_subscript	Slicing (returns a new memoryview)
1101-1400	memory_cast	Change format/shape interpretation
1401-2000	tobytes, tolist, toreadonly	Conversion helpers

Reading

Buffer info

// CPython: Objects/memoryobject.c:42 Py_buffer
typedef struct bufferinfo {
    void *buf;             /* pointer to raw memory */
    PyObject *obj;         /* owner of the buffer */
    Py_ssize_t len;        /* total byte count */
    Py_ssize_t itemsize;   /* size of one element */
    int readonly;
    int ndim;              /* number of dimensions */
    char *format;          /* struct format string (e.g. "B", "d") */
    Py_ssize_t *shape;     /* elements per dimension */
    Py_ssize_t *strides;   /* byte step per dimension */
    Py_ssize_t *suboffsets; /* for indirect arrays */
} Py_buffer;

memory_cast

// CPython: Objects/memoryobject.c:1360 memory_cast
static PyObject *
memory_cast(PyMemoryViewObject *self, PyObject *args, PyObject *kwds)
{
    /* Change format and shape, keeping the same underlying memory */
    PyObject *format;
    PyObject *shape = NULL;
    if (!PyArg_ParseTuple(args, "O|O:cast", &format, &shape))
        return NULL;
    /* Validate: total bytes must stay the same */
    ...
    return PyMemoryView_FromBuffer(&newinfo);
}

mv.cast('d') reinterprets the bytes as double values. The total byte count must remain unchanged.

tobytes

// CPython: Objects/memoryobject.c:1650 memory_tobytes
static PyObject *
memory_tobytes(PyMemoryViewObject *self, PyObject *args, PyObject *kwds)
{
    /* If contiguous C-order, copy directly */
    if (MV_C_CONTIGUOUS(self->flags)) {
        return PyBytes_FromStringAndSize(self->view.buf, self->view.len);
    }
    /* Otherwise, iterate with strides */
    ...
}

gopy notes

memoryview is needed for struct.pack_into, bytes.fromhex, and zero-copy I/O. In gopy memoryview wraps a Go []byte slice (or a pointer+length pair for C-origin buffers). The cast and shape operations are implemented in objects/memory.go. tobytes returns a Python bytes object by copying the buffer.