A custom range dictionary using bisect

range_dict.py

class RangeDict(dict):
    """ A dictionary mapping a key to a range of integers """
    
    def __getitem__(self, key):
        sorted_keys = sorted(self.keys())
        idx = bisect.bisect_right(sorted_keys, key)
        # Mapped key is one down from index but we don't
        # want to cycle using negative indices
        if idx > 0: idx -= 1
        mapped_key = sorted_keys[idx]
        return super().__getitem__(mapped_key)