A GtkTreeIterCompareFunc should return a negative integer, zero, or a positive
integer if a sorts before b, a sorts with b, or a sorts after b
respectively.
If two iters compare as equal, their order in the sorted model
is undefined. In order to ensure that the gtk.tree_sortable.TreeSortable behaves as
expected, the GtkTreeIterCompareFunc must define a partial order on
the model, i.e. it must be reflexive, antisymmetric and transitive.
For example, if model is a product catalogue, then a compare function
for the “price” column could be one which returns
price_of(a) - price_of(b).
A GtkTreeIterCompareFunc should return a negative integer, zero, or a positive integer if a sorts before b, a sorts with b, or a sorts after b respectively.
If two iters compare as equal, their order in the sorted model is undefined. In order to ensure that the gtk.tree_sortable.TreeSortable behaves as expected, the GtkTreeIterCompareFunc must define a partial order on the model, i.e. it must be reflexive, antisymmetric and transitive.
For example, if model is a product catalogue, then a compare function for the “price” column could be one which returns price_of(a) - price_of(b).