This decorator works by storing the time just before the function starts running (at the line marked # 1) and just after the function finishes (at # 2). The time the function takes is then the difference between the two (at # 3). We use the time.perf_counter() function, which does a good job of measuring time intervals. Here are some examples of timings:
John Mansell Smith has been a self-employed painter & decorator for four years. He explains what it’s like to run your own business. “I became a self-employed painter & decorator when I took early retirement from my professional job in London, where I was employed as a Principal Building Surveyor. When I retired, I needed some additional income to supplement my pension, and having been in the building industry I was fully aware of the standard and quality which would be required to produce work to a professional standard. For a typical day at work, I usually arrive at the job at 8.30 am, and then depending on the sort of work I am doing it will vary a great deal. I could be undertaking external decorations or internal decorations, but in each case it would require covering and protecting the client's furniture, preparation of surfaces, washing down the walls, painting, wallpapering, cleaning up, etc. I try to leave at about 4.30 pm, but this may vary depending on the stage that I have reached with the job. In terms of likes and dislikes, I don’t enjoy working outside in poor weather, although I try to plan my workload to avoid this. However, I do like the freedom of being my own boss and getting complimented on a good job. If you wanted to be a painter and decorator, you would have to decide whether you wish to work for a company with the benefits such as holiday pay, but with the constraints of not being your own boss, or working for yourself with the freedom this gives but also the uncertainty of workload. As a self-employed person I can charge about £15 per hour for work that I do on an hourly rate, or I base any calculations on this rate when I am producing an estimate for a client. In attempting to find work, I would try the job centre, trade journals, large decorating companies, the internet and building training boards. To do the job you need to be a clean, neat worker with an eye for detail. The job you produce is the final result that the client will see, so it is vital that you can produce a finished job that you would be happy to have in your own home.
Now we have our logit decorator in production, but when some parts of our application are considered critical, failure might be something that needs more immediate attention. Let’s say sometimes you want to just log to a file. Other times you want an email sent, so the problem is brought to your attention, and still keep a log for your own records. This is a case for using inheritence, but so far we’ve only seen functions being used to build decorators.
The decorator pattern can be used to extend (decorate) the functionality of a certain object statically, or in some cases at run-time, independently of other instances of the same class, provided some groundwork is done at design time. This is achieved by designing a new Decorator class that wraps the original class. This wrapping could be achieved by the following sequence of steps:
The .__init__() method must store a reference to the function and can do any other necessary initialization. The .__call__() method will be called instead of the decorated function. It does essentially the same thing as the wrapper() function in our earlier examples. Note that you need to use the functools.update_wrapper() function instead of @functools.wraps.