Fix get_by_point for python 3

[mmeyer724]

In Python 3, calling values() on a dict returns dict_values, which does not support the sort method. This leads to the following error under Python 3: AttributeError: 'dict_values' object has no attribute 'sort'

Additionally, map now returns a generator instead of a list, so the [:] slice syntax doesn't work 🙁: TypeError: 'map' object is not subscriptable

I addressed this by using itertool's islice function instead.

[jonthornton]

Thank you!