[enhancement] Add function is_singleton

[gfitas]

Hello,

I was wondering if it will be possible to add a function that could say if an interval is a singleton or not ?
For the moment I just did i.lower==i.upper but I found it dirty. A solution with a function is_singleton will be more elegant.

Thank you in advance

[AlexandreDecan]

Hello,

That's feasible ;) I've two questions in mind then:

1. Shouldn't we also add is_left_open, is_right_open, is_left_closed, is_right_closed, is_left_bounded, is_right_bounded so we have a "full" set of property checkers?
2. Should we add them as functions, or as methods (e.g. like i.is_empty). The latter seems more adequate...

[AlexandreDecan]

I'm currently considering making lower, left, right and upper available on Interval instances as well. As such, it won't be required to access the underlying AtomicInterval instances of an Interval instance to perform some common checks:

>>> x = I.openclosed(-I.inf, 0)
>>> # Check for left/right closed
>>> x.left == I.CLOSED, x.right == I.CLOSED
(False, True)
>>> # Check if interval is left/right bounded
>>> x.lower == -I.inf, x.upper == I.inf
(True, False)
>>> # Check for singleton
>>> x.lower == x.upper
False

[AlexandreDecan]

Does the change solve your problem? It allows you to do i.lower == i.upper instead of i.to_atomic().lower == i.to_atomic().upper or even i[0].lower == i[-1].upper.

I know that you found i.lower == i.upper "ugly", but it is the (second) most obvious piece of code to check for a singleton (the first one being is_singleton, but I don't think it really adds value to the library). I'm waiting for your feedback before pushing the changes.

[AlexandreDecan]

I merged the changes to master, among other (many) changes that should ease intervals transformations and modifications.

I'll release 1.8.0 tomorrow unless these changes do not solve this issue.