Create and Use Custom Decorators

How to create and use your own custom decorators.

A decorator uses another concept of programming called first-class functions. Essentially it allows you to treat a function as a variable by passing it to another function.

The structure of a decorator is pretty simple. The decorator is given a name and you can then choose to either do some actions before executing the inner function (the one that gets passed in) or after, or both. It's easier to explain by example

A decorator is defined with the keyword decorator followed by the name of the decorator. After that it works like a normal function except fo one thing. You can call inner() somewhere in the decorator body, this is where the "passed in" function (the one the decorator is used on) will get executed. You can put any code before or after this function, you can also execute inner() multiple times or e.g. in a loop.

Then put & and the name of a decorator to decorate any function.

Example

decorator my_first_decorator:
  print('Before')
  inner()
  print('After')

&my_first_decorator
def my_function(message):
  print(message)

my_function('Hello')

The output of this program would be:

Before
Hello
After

As you can see what happened is that the function my_function got passed into my_first_decorator, which then first printed "Before" then ran the "inner" function, and then printed "After".