In a typical use of options, your highly-functional class defines default values. Subclasses can add, remove, or override options. Instances use class defaults, but they can be overridden when each instance is created. For any option an instance doesn’t override, the class default “shines through.”

So far, this isn’t very different from a typical use of Python’s standard instance and class variables. The next step is where options gets interesting.

Individual method calls can similarly override instance and class defaults. The options stated in each method call obtain only for the duration of the method’s execution. If the call doesn’t set a value, the instance value applies. If the instance didn’t set a value, the class default applies (and so on, to its superclasses, if any).

One step further, Python’s with statement can be used to set option values for just a specific duration. As soon as the with block exists, the option values automagically fall back to what they were before the block. (In general, if any option is unset, its value falls back to what it was in the next higher layer.)

To recap: Python handles class, subclass, and instance settings. options handles these as well, but also adds method and transient settings. By default when Python overrides a setting, it’s destructive; the value cannot be “unset” without additional code. When a program using options overrides a setting, it does so non-destructively, layering the new settings atop the previous ones. When attributes are unset, they immediately fall back to their prior value (at whatever higher level it was last set).