like Mongodb's ObjectID

object_id.py

# coding:utf8
# object_id.py

__all__ = ('ObjectID', )

from __future__ import print_function
from __future__ import unicode_literals

import os
import struct
import socket
import sys
from hashlib import md5
import time
import itertools
import binascii

PY3 = sys.version_info[0] == 3

def _object_id():
    range_ = range
    if not PY3:
        range_ = xrange
    iter_ = itertools.cycle(range_(0xffffff))
    machine = md5(socket.gethostname().encode('utf8')).digest()[:3]
    pid = struct.pack('>L', os.getpid())
    def f(as_bytes=False):
        now = struct.pack('>L', int(time.time()))
        inc = struct.pack('>L', next(iter_))[1:]
        result = b''.join(
            (now, machine, pid, inc)
        )
        return result
    return f

object_id = _object_id()

class ObjectID(object):
    def __init__(self, val=None):
        if not val:
            self.bytes = object_id()
        elif type(val) is bytes:
            self.bytes = val
        else:
            self.string = val

    @property
    def string(self):
        return self._string

    @string.setter
    def string(self, val):
        self._string = val
        self._bytes = binascii.unhexlify(val)

    @property
    def bytes(self):
        return self._bytes

    @bytes.setter
    def bytes(self, val):
        self._bytes = val
        self._string = binascii.hexlify(val).decode('utf8')


    def __str__(self):
        return self.string

    if PY3:
        def __eq__(self, b):
            return self.bytes == b.bytes
    else:
        def __cmp__(self, b):
            return not self.bytes == b.bytes


if __name__ == '__main__':
    a = ObjectID()
    b = ObjectID(a.string)
    c = ObjectID(a.bytes)

    print(a==b)
    print(a==c)

    d = ObjectID()

    print(a==d)
    list(map(print, (a, b, c, d)))