Real World Instrumentation with Python

Chapter 12. Reading and Writing Data Files

Two people were examining the output of the new computer in their department. After an hour or so of analyzing the data, one of them remarked: “Do you realize it would take 400 people at least 250 years to make a mistake this big?”

—Anonymous

Being able to acquire data is good, but being able to save it in a file so it can be analyzed and archived is even better. Simple applications, such as an electronic thermostat, might not have an obvious need to save data, but data acquired and saved by even the simplest applications may provide valuable insight into long-term trends. In Chapter 10 we saw how to use a simulator that could save the results of a simulation into an ASCII file for later review and analysis. In this chapter we’ll take a closer look at how that can be accomplished, and we’ll also look at some other ways to save data.

For example, consider what you might be able to learn if the thermostat in your home could record the outside ambient temperature, the inside temperature, the set-points, the activity of the heater and air conditioner units, and the control settings. With this data you would be able to see how well your heater or air conditioner is handling temperature control, what kind of duty cycle it has, and if someone is overriding the fan on a regular basis. What it could tell you might just surprise you, especially if you could collect the data continuously for a year or two.

Data can exist in many different forms. In some ...