Adding a parameter to a decorator

A common requirement is to customize a decorator with additional parameters. Rather than simply creating a composite 

, we can do something a bit more complex. With parameterized decorators, we can create 

. We've applied a parameter, c, as part of creating the wrapper,

. This parameterized composite function,

, can then be used with the actual data, x.

In Python syntax, we can write it as follows:

@deco(arg)
def func(x):
    something

There are two steps to this. The first step applies the parameter to an abstract decorator to create a concrete decorator. Then the concrete decorator, the parameterized deco(arg) function, is applied to the base function definition to create the decorated function.

The effect is as follows:

def func(x):
    return something(x)
concrete_deco = deco(arg)
func= concrete_deco(func)

We've done three things, and they are as follows:

1. Defined a function, func().
2. Applied the abstract decorator, deco(), to its argument, arg, to create a concrete...