Python module: segfault on exit when hierarchy iterators are alive

[klayoutmatthias]

This code makes Python / klayout module segfault on exit:

import klayout.db as kdb
ly = kdb.Layout()
cell = ly.create_cell("TOP")
parents = cell.each_parent_cell()

Root cause is the Python finalization code which first deletes the Layout and then the iterator pointing to is.

A simple workaround is to make sure the iterator ("parents") is removed before finalization:

import klayout.db as kdb
ly = kdb.Layout()
cell = ly.create_cell("TOP")
parents = cell.each_parent_cell()
...
parents = None