Recursive dict reversal in Python

invert_recursive_dict.py

def invert_recursive_dict(d: Dict) -> Dict:
    """
    Assuming `d` is a recursive Dict, invert it by mapping its leaves to the 
    lists/paths of keys leading to them in the original dict.
    """
    def invert(d, path: List, acc: Dict):
        if isinstance(d, Dict):
            # Handle dict contents recursively
            for k, i in d.items():
                invert(i, path+[k], acc)
        else:
            # Arrived at leaf - store in the inverted dict
            acc[d] = path
        return acc
    return invert(d, [], {})
  
# Example

BITS_TO_JMP_INSTR = {
    # B2  B1  B0
    False: {
        False: {
            False: None,
            True: "JGT",
        },
        True: {
            False: "JEQ",
            True: "JGE",
        },
    },
    True: {
        False: {
            False: "JLT",
            True: "JNE",
        },
        True: {
            False: "JLE",
            True: "JMP",
        },
    },
}

# invert_recursive_dict(BITS_TO_JMP_INSTR)
# ->
# {
#     None: [False, False, False],
#     "JGT": [False, False, True],
#     "JEQ": [False, True, False],
#     "JGE": [False, True, True],
#     "JLT": [True, False, False],
#     "JNE": [True, False, True],
#     "JLE": [True, True, False],
#     "JMP": [True, True, True],
# }

Written as an exploration of various ways to represent the bit structures of machine instructions as part of the Nand2Tetris course.