
make sure a file-based index is overwriteable.

    >>> from rtree.index import Rtree
    >>> r = Rtree('overwriteme')
    >>> del r    
    >>> r = Rtree('overwriteme', overwrite=True)


the default serializer is pickle, can use any by overriding dumps, loads

    >>> r = Rtree()
    >>> some_data = {"a": 22, "b": [1, "ccc"]}
    >>> try: 
    ...     import simplejson
    ...     r.dumps = simplejson.dumps
    ...     r.loads = simplejson.loads
    ...     r.add(0, (0, 0, 1, 1), some_data)
    ...     list(r.nearest((0, 0), 1, objects="raw"))[0] == some_data
    ... except ImportError: 
    ...     # "no import, failed"
    ...     True
    True


    >>> r = Rtree()
    >>> r.add(123, (0, 0, 1, 1))
    >>> item = list(r.nearest((0, 0), 1, objects=True))[0]
    >>> item.id
    123

    >>> r.valid()
    True
