TextIter.editable

Returns whether the character at iter is within an editable region of text. Non-editable text is “locked” and can’t be changed by the user via #GtkTextView. This function is simply a convenience wrapper around [gtk.text_iter.TextIter.getAttributes]. If no tags applied to this text affect editability, default_setting will be returned.

You don’t want to use this function to decide whether text can be inserted at iter, because for insertion you don’t want to know whether the char at iter is inside an editable range, you want to know whether a new character inserted at iter would be inside an editable range. Use [gtk.text_iter.TextIter.canInsert] to handle this case.