added repr to orbits and fixed orbitalelements.ipynb

[dtamayo]

Fixed OrbitalElements.ipynb to new syntax of sim.particles[i].orbit().

Also added a repr to the Orbit class so when we finish a cell with e.g.

sim.particles[1].orbit()

it will give us useful information instead of just Orbit object at memory loc X

[hannorein]

Thanks! Couldn't __repr__ just call __str__? I see there is a conceptual difference between the two but we're not making use of it right now. (We could in principle, __str__ could output something like "eccentric orbit" or "hyperbolic orbit" to make it more human-interpretable)

[dtamayo]

Good point...I actually just deleted __str__. I just looked up that the behavior is that if there is no __str__, __repr__ gets called (e.g. when doing print(orb)), but it doesn't go the other way (you need a __repr__ to not get blah obj at memory loc X) . So maybe it's less redundant to just define a `__repr__1? Unless like you say, we want to get different output when we end a cell with

ps[1].orbit()

vs

print(ps[1].orbit())

[hannorein]

makes sense!

(Don't know why the REBOUNDx trigger fails)

[dtamayo]

emailed you