In the C API, PyMemoryViewObject has a mbuf.master attribute, Include/memoryview.h:

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typedef struct {
    PyObject_HEAD
    int flags;          /* state flags */
    Py_ssize_t exports; /* number of direct memoryview exports */
    Py_buffer master; /* snapshot buffer obtained from the original exporter */
} _PyManagedBufferObject;


/* memoryview state flags */
#define _Py_MEMORYVIEW_RELEASED    0x001  /* access to master buffer blocked */
#define _Py_MEMORYVIEW_C           0x002  /* C-contiguous layout */
#define _Py_MEMORYVIEW_FORTRAN     0x004  /* Fortran contiguous layout */
#define _Py_MEMORYVIEW_SCALAR      0x008  /* scalar: ndim = 0 */
#define _Py_MEMORYVIEW_PIL         0x010  /* PIL-style layout */

typedef struct {
    PyObject_VAR_HEAD
    _PyManagedBufferObject *mbuf; /* managed buffer */
    Py_hash_t hash;               /* hash value for read-only views */
    int flags;                    /* state flags */
    Py_ssize_t exports;           /* number of buffer re-exports */
    Py_buffer view;               /* private copy of the exporter's view */
    PyObject *weakreflist;
    Py_ssize_t ob_array[1];       /* shape, strides, suboffsets */
} PyMemoryViewObject;
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