ATR is the average true range. So the type of average and the period of the average are inputs. Unless of course everything is set to default and one is not interested to try other settings.
Some free Python courses on Udemy:
https://www.udemy.com/ardit-sulce-python-for-beginners/
https://www.udemy.com/deep-learning-prerequisites-the-numpy-stack-in-python/
Mind saying if you use indicators, or patterns/price action, or some sort of statistics? Also, are you day-trading or swing-trading, and what type of markets. Thanks.