Index is checking write access despite assuming read-only access

[LuckyLub]

Context

When passing a filename to the Index class, it assumes that the file can not be overwritten unless explicitly set by the user.

rtree/rtree/index.py

Lines 240 to 244 in 81cc81a

	# assume if the file exists, we're not going to overwrite it
	# unless the user explicitly set the property to do so
	if os.path.exists(p):
	self.properties.overwrite = bool(kwargs.get("overwrite", False))

However, passing a file which is in a read-only dir is not allowed, since it is checked if the provided file is within a directory with write access.

rtree/rtree/index.py

Lines 255 to 256 in 81cc81a

	if not os.access(d, os.W_OK):
	message = "Unable to open file '%s' for index storage" % f

Expected behavior

When the provided file is within a read-only directory, but overwrite self.properties.overwrite = False the no OSError should be raised.

[jason-curtis]

This is also causing problems for me - my .idx is pre-cached and not writeable since I'm running on AWS Lambda. I can copy the files out to the .tmp directory but I'd rather not!

[jason-curtis]

I took a crack at this in #281, removing the check in rtree. Unfortunately the same check is happening in libspatialindex when we call down to the C code: https://libspatialindex.org/en/latest/doxygen/DiskStorageManager_8cc_source.html#l00173 .

So we could remove the checks on the Python level, but this would need to be pushed to the libspatialindex maintainers.

[mwtoews]

You could raise an issue and/or PR for libspatialindex; the source code on GitHub is here