Getting container/parent object from within python

Pass a reference to the Bar object, like so:

class Foo(object):
    def __init__(self):
        self.text = "Hello World"  # has to be created first, so Bar.__init__ can reference it
        self.bar = Bar(self)

class Bar(object):
    def __init__(self, parent):
        self.parent = parent
        self.newText = parent.text

foo = Foo()

Edit: as pointed out by @thomleo, this can cause problems with garbage collection. The suggested solution is laid out at http://eli.thegreenplace.net/2009/06/12/safely-using-destructors-in-python/ and looks like

import weakref

class Foo(object):
    def __init__(self):
        self.text = "Hello World"
        self.bar = Bar(self)

class Bar(object):
    def __init__(self, parent):
        self.parent = weakref.ref(parent)    # <= garbage-collector safe!
        self.newText = parent.text

foo = Foo()

is it possible to get the object, say Foo, that contains another object, Bar, from within Bar itself?

Not "automatically", because the language isn't built like that, and in particular, the language is built such that there is no way to guarantee that Foo exists.

That said, you can always do it explicitly. Attributes, like every other identifier in Python, are just names, not storage space for data; so nothing prevents you from letting the Bar instance have a manually assigned foo attribute that is a Foo instance, and vice-versa at the same time.