import collections.abc

class struct_array_view(collections.abc.MutableSequence):

    def __init__(self, struct, data):
        self._struct = struct
        self._data = data
        self._size = struct.calcsize()

    def __len__(self):
        if len(self._data) % self._size:
            raise ValueError()
        return len(self._data) // self._size

    def __getitem__(self, i):
        return self._struct.unpack(self._data[self._getslice(i)])

    def __setitem__(self, i, value):
        self._data[self._getslice(i)] = self._struct.pack(*value)

    def __delitem__(self, i):
        del self._data[self._getslice(i)]

    def __iter__(self):
        i = 0
        while i < len(self._data):
            yield self._struct.unpack(self._data[i: i + self._size])
            i += self._size

    def __reversed__(self):
        if len(self._data) % self._size:
            raise ValueError()
        for i in range(len(self._data), 0, -self._size):
            yield self._struct.unpack(self._data[i - self._size: i])

    def insert(self, i, item):
        self._data.insert(i * self._size, item)

    def _getslice(self, i):
        return slice(i * self._size, (i + 1) * self._size)