How to do in-place object replacement in python

obj_replacement.py

from __future__ import print_function


_id_seq = 1

def id_seq():
    global _id_seq
    num = _id_seq
    _id_seq += 1
    return num


class Test(object):
    def __init__(self, arg, id=id_seq()):
      self.id = id
      self.arg = arg

    # this method is the star of the show and the
    # reason this whole thing is interesting
    def update(self, new_arg):
        # we replace the current instance with the
        # content of a new instance, so all references
        # to the old instance will return the new instance
        new_inst = Test(new_arg, id=self.id)
        self.__dict__.update(new_inst.__dict__)

        
# LET'S TEST THIS OUT!

# we create some test instances
t1 = Test('t1')
t2 = Test('t2')
t3 = Test('t3')

# we put all the test instances in to a dict, as
# that will store one of our references
d = {t.id: t for t in [t1, t2, t3]}

# let's see what we have
print(d)
[print(item.arg) for item in d.values()]

# now we update using one of our two stored references
t1.update('t4')
t2.update('t5')
t3.update('t6')

# we can delete these references to show the
# dict ones are different
del t1
del t2
del t3

# now let's print the dict again
print(d)
[print(item.arg) for item in d.values()]