Objects/memoryobject.c

Source:

cpython 3.14 @ ab2d84fe1023/Objects/memoryobject.c ↗

Objects/memoryobject.c implements the memoryview type. A memoryview is a window into another object's buffer without copying the data. The file covers buffer acquisition and release, the Py_buffer struct, shape and strides arithmetic for multi-dimensional views, slicing, the cast() method for reinterpreting bytes as a different format, and comparison.

Map

Lines	Symbol	Role
1-200	Py_buffer helpers	PyBUF_* flag checking, buffer acquire/release wrappers
201-600	PyMemoryViewObject internals	mbuf master buffer, view lifetime tracking
601-1200	Index and slice	memory_subscript, memory_ass_subscript
1201-1800	memory_cast	Reinterpret bytes as new format/shape
1801-2400	Comparison	memory_richcompare, element-by-element compare
2401-3000	Type slot wiring	PyMemoryView_Type, Py_buffer protocol export

Reading

Buffer acquisition

PyMemoryView_FromObject calls PyObject_GetBuffer on the source object, which invokes tp_as_buffer->bf_getbuffer. The resulting Py_buffer struct describes the memory region: pointer, length, item size, format string (struct-style), and optional shape/strides arrays.

// Objects/memoryobject.c:201 PyMemoryView_FromObject
PyObject *
PyMemoryView_FromObject(PyObject *v)
{
    PyMemoryViewObject *mv;
    Py_buffer *base;
    if (PyMemoryView_Check(v)) {
        mv = (PyMemoryViewObject *)v;
        base = &mv->view;
        return PyMemoryView_FromMemory(base->buf, base->len, PyBUF_WRITE);
    }
    return PyMemoryView_FromBuffer(/* ... */);
}

Each memoryview holds a mbuf reference to a master buffer object that tracks the original exporter, preventing the underlying memory from being freed while any view is alive.

Slicing and strides

For contiguous 1-D buffers, slicing adjusts the buf pointer and len field directly. For multi-dimensional views, slicing adjusts the shape and strides arrays, enabling zero-copy row/column access into NumPy-style arrays.

// Objects/memoryobject.c:601 memory_subscript (simplified)
static PyObject *
memory_subscript(PyMemoryViewObject *self, PyObject *key)
{
    Py_buffer *view = &self->view;
    if (view->ndim == 1) {
        // fast path: single integer or slice
    } else {
        // multi-dimensional: update shape/strides
    }
}

cast()

memory_cast reinterprets the bytes using a new format string and optional shape. The total byte count must be identical. The cast is zero-copy and returns a new memoryview backed by the same mbuf.

// Objects/memoryobject.c:1201 memory_cast
static PyObject *
memory_cast(PyMemoryViewObject *self, PyObject *args, PyObject *kwds)
{
    /* validate new format/shape, share mbuf */
}

gopy notes

Not yet ported. The planned package path is objects/memoryview.go. gopy would represent Py_buffer as a Go struct with a []byte slice plus shape/strides slices, and implement GetBuffer/ReleaseBuffer as methods on exporters. The zero-copy guarantee maps to passing a slice header rather than copying bytes.