ENH: use @cached_property

[glyg]

Where necessary, i.e for topology dependant indexing elements

https://pypi.python.org/pypi/cached-property

then complete reset_topo by flushing (del the property in self.__dict__ like indicated in the examples)

[glyg]

This is deferred to a new optimization campaign

[glyg]

latest optimization shows, imho, that this might not be a good way to optimize. In order to avoid repeated calls to upcast, storing the values directly in edge_df seems a better and easier practice. Closing