We can create a context manager class, which is a factory for an application object. This gives us a pleasant separation of design considerations without cluttering up an application class with context management features.

Let's say we want a deterministic Deck for dealing in blackjack. This isn't as useful as it might sound. For unit testing, we'll need a completely mock deck with specific sequences of cards. This has the advantage that the context manager works with the classes we already saw.

We'll extend the simple context manager shown earlier to create a Deck that can be used within the with statement context.

The following is a class that is a factory for Deck and also tweaks the random module:

class Deterministic_Deck:
    def __init__( self, *args, **kw ):
        self.args= args
        self.kw= kw
    def __enter__( self ):
        self.was= random.getstate()
        random.seed( 0, version=1 )
        return Deck( *self.args, **self.kw )
    def __exit__...