demo.py

# -*- coding: utf-8 -*-

todo = [
    {"a": 1, "b": 1},
    {"a": 2, "b": 2},
    {"a": 1, "b": 1},
    {"a": 0, "b": 1},
    {"a": 2, "b": 2},
    {"a": 0, "b": 2},
    {"a": 2, "b": 2},
]


def gen_key_list(item_list):
    for o in item_list:
        yield (o.get('a', None), o.get('b', None))


def find(item_list):
    idx = -1
    output_idx = []
    first_idx = {}
    exists = set()
    for key in gen_key_list(item_list):
        idx += 1
        if key in exists:
            if key in first_idx:
                output_idx.append(first_idx[key])
                del first_idx[key]
            output_idx.append(idx)
        else:
            first_idx[key] = idx
            exists.add(key)

    return [item_list[idx] for idx in output_idx]


if __name__ == '__main__':
    print(find(todo))