from collections import defaultdict
import weakref

class KeepRefs(object):
    __refs__ = defaultdict(list)
    def __init__(self):
        self.__refs__[self.__class__].append(weakref.ref(self))

    @classmethod
    def get_instances(cls):
        for inst_ref in cls.__refs__[cls]:
            inst = inst_ref()
            if inst is not None:
                yield inst

class Person(KeepRefs):
    def __init__(self, numder, full_name, data_birs, sex, data_start_work, post, pay=0):
        super(Person, self).__init__()
        self.numder=numder
        self.full_name=full_name
        self.data_birs=data_birs
        self.sex=sex
        self.data_start_work=data_start_work
        self.post=post
        self.pay=pay

first=Person(1, 'Nemkovych Roman', '15.10.1995', 'men', '01.01.2017', 'developer', 1500)
second=Person(2, 'Ivanov Ivan', '11.12.1980', 'men', '28.03.2015', 'developer', 15000)
third=Person(3, 'Diego God', '01.01.2000', 'women', '01.01.2017', 'TestOOP', 2000)

for r in Person.get_instances():
    print(r.full_name)