import weakref, inspect
class MetaInstanceTracker(type):
def __new__(cls, name, bases, ns):
t = super(MetaInstanceTracker, cls).__new__(cls, name, bases, ns)
t.__instance_refs__ = []
return t
def __instances__(self):
instances = [(r, r()) for r in self.__instance_refs__]
instances = filter(lambda (x,y): y is not None, instances)
self.__instance_refs__ = [r for (r, o) in instances]
return [o for (r, o) in instances]
def __call__(self, *args, **kw):
instance = super(MetaInstanceTracker, self).__call__(*args, **kw)
self.__instance_refs__.append(weakref.ref(instance))
return instance
class InstanceTracker:
__metaclass__ = MetaInstanceTracker
class MetaAutoReloader(MetaInstanceTracker):
def __new__(cls, name, bases, ns):
new_class = super(MetaAutoReloader, cls).__new__(
cls, name, bases, ns)
f = inspect.currentframe().f_back
for d in [f.f_locals, f.f_globals]:
if d.has_key(name):
old_class = d[name]
for instance in old_class.__instances__():
instance.change_class(new_class)
new_class.__instance_refs__.append(
weakref.ref(instance))
# this section only works in 2.3
for subcls in old_class.__subclasses__():
newbases = ()
for base in subcls.__bases__:
if base is old_class:
newbases += (new_class,)
else:
newbases += (base,)
subcls.__bases__ = newbases
break
return new_class
class AutoReloader:
__metaclass__ = MetaAutoReloader
def change_class(self, new_class):
self.__class__ = new_class
class Bar(AutoReloader):
pass
class Baz(Bar):
pass
b = Bar()
b2 = Baz()
class Bar(AutoReloader):
def meth(self, arg):
print arg
if __name__ == '__main__':
# now b is "upgraded" to the new Bar class:
b.meth(1)
# new in 2.3, Baz instances join the fun:
b2.meth(2)
# new Baz() instances now play too:
Baz().meth(3)
