key manager for dict (unique key autogeneration)

# -*- coding: utf-8 -*-
#-------------------------------------------------------------------------------
# Name:        r_manager
# Purpose:
#
# Author:      User
#
# Created:     03.07.2020
# Copyright:   (c) User 2020
# Licence:     <your licence>
#-------------------------------------------------------------------------------

import itertools
import time
import datetime

class RequestManager:

    def __init__(self, _dct=None):
        self._dict = _dct or {}
        self.removed = []
        self._next = (max(self._dict.keys()) + 1) if self._dict else 0

    def pop(self, key):
        val = self._dict.pop(key, None)
        if val: self.removed.append(key)
        return val

    def append(self, values):
        key = self._get_next()
        self._dict[key] = values
        return key

    def _get_next(self):
        if len(self.removed) > 0:
            key = self.removed.pop()
            return key
        else:
            _next = self._next
            self._next += 1
            return _next


    # has_key
    # del


def main():

    d = {}
    for i in range(1000000): d[i]=(i+1, datetime.time)


    t = time.clock()

    r_manager = RequestManager(d)
    skey = 000001

    # (skey) # request_time, refresh_token
    # skey  - секретный ключ
    # дата создания (нужна для очистки неиспользуемых ключей).
    r_manager.append((skey, datetime.time))


    print(time.clock() - t)


    t = time.clock()

    print r_manager.pop(1)

    print(time.clock() - t)

if __name__ == '__main__':
    main()