Smart is_displayed

Currently, we have is_displayed that only returns true or false without further explanation. It would be helpful to see which exact part of the is_displayed failed. Therefore I would propose this:

• Create a descriptor that will be set as is_displayed instead of the property and will hold a set of rules/checks for the displayed check.
• The descriptor would implement __nonzero__ to act as a boolean value, therefore making it usable in if and such expressions.
• On the __nonzero__ resolution it would store the result of each partial check in some sort of dictionary.
• It would provide a method that would either directly raise an exception or just provide an information about those checks that did not pass.

if not view.is_displayed:
    raise Exception(view.is_displayed.why)

Or something like that, this is just a concept. (the sample provided would have caching problems)

The rules would be flexible - a string could represent either widget name (it would call is_displayed on that one) or if it would not be a widget then it would assume it is an attribute to be read. It could also provide some basic checkers like you could do a value comparison ... the discussion is open.

Start by locating the existing is_displayed implementation and reviewing how its current boolean result is used. Define the descriptor behavior, diagnostic information, rule format, and caching expectations before implementation; done means failed checks can be identified without breaking existing boolean-style usage.