Sample of reloading a class definition in python. Old and new instances point to the correct class definition.

py-code-update.py

# writing c1 class definition to module mod1
cs = """
class c1(object):
    att = 1
    def m1(self):
        self.__class__.att += 1
        # printing class name, class-id, and the id of the class, which happens to be its memory address
        print "uno:", self.__class__, "class-id:", id(self.__class__), "att:", self.__class__.att         
"""

f = open('mod1.py', 'w')
f.write(cs)
f.close()

import mod1
from mod1 import c1

# creating instance 1 of class 1
i1 = mod1.c1()
i1.m1()
i1.m1()

# now we are going to update our c1 class definition
# so that the python interpreter realizes the class definition has changed:
# we have to either delete the .pyc (python compiled) file, or sleep 1 second so that .py and .pyc files have different date.

#from time import sleep
#sleep(1)

import os
os.remove('mod1.pyc')


# changing c1 class definition
cs2 = """
class c1(object):
    att = 1000
    def m1(self):
        self.__class__.att += 1
        # printing class name, class-id, and the id of the class, which happens to be its memory address
        print "dos:", self.__class__, "class-id:", id(self.__class__), "att:", self.__class__.att         
"""

f = open('mod1.py', 'w')
f.write(cs2)
f.close()

# force reload class changes from filesystem
reload(mod1)
import mod1
from mod1 import c1

# creating instance 2 of class 1
i2 = mod1.c1()

# now, the behaviour of i1 and i2 match their original class definitions, not current c1.
i2.m1()
i1.m1()