A healthy and happy snake will shed in one piece. Once shedding starts, it shoudnt take longer than an hour.
If your python has retained parts of its old skin, you must get it off.
Get a bucket of warm water (around 30 degrees) and soak your python in it for around 5 to 10 minutes.
You will have to stand there and hold it in if nessesary. Then with a soft cloth, gentley wipe the loosened skin off.
After you have all the old skin off, give it a good feed and leave it be for a week.
There are a few reasons why a python is having shedding problems, it could be stress,
type of substreight, heating / humidity ect.
If its a new addition, give it time to settle in. If its next shed isnt clean, you will have to have a good look at your set up.