class Array(object):    def __init__(self, size=32):        self._size=size        self._item=[None]*size    def __getitem__(self, item):        return self._item[item]    def __setitem__(self, key, value):        self._item[key]=value    def __len__(self):        return self._size    def clear(self):        for i in range(self._size):            self._item[i]=None    def __iter__(self):        for i in self._item:            yield idef test_array():    size=10    a=Array(size)    a[0]=1    assert a[0]==1    a.clear()    assert a[0] is None