How to reload the code of a method of class object in Python?

Question

I\'m find a way to reload the method of a class object at runtime，here is the example: I have define a class A firstly which lies on the file test.py.

class          


        

Answer 1

You have to reload your module from the fresh code, get the class and assign it back to the instance:

import sys
def update_class(instance):
  cls=instance.__class__
  modname=cls.__module__
  del sys.modules[modname]
  module=__import__(modname)
  instance.__class__=getattr(module,cls.__name__)

While developing and updating the code you could use the same trick to define instances that reload their class anytime they are used.

import sys

class ObjDebug(object):
  def __getattribute__(self,k):
    ga=object.__getattribute__
    sa=object.__setattr__
    cls=ga(self,'__class__')
    modname=cls.__module__ 
    mod=__import__(modname)
    del sys.modules[modname]
    reload(mod)
    sa(self,'__class__',getattr(mod,cls.__name__))
    return ga(self,k)

class A(ObjDebug):
   pass

a=A()

If you edit the code of A to add a method, then you can use it without instantiating again a.

Actually del sys.modules[modname] seems to create nasty bugs for which some symbols becomes None objects from one line to the other. (not understood why)