Data Visualization with Python and JavaScript, 2nd Edition

Chapter 3. Reading and Writing Data with Python

One of the fundamental skills of any data visualizer is the ability to move data around. Whether your data is in an SQL database, a comma-separated value (CSV) file, or in some more esoteric form, you should be comfortable reading the data, converting it, and writing it into a more convenient form if need be. One of Python’s great strengths is how easy it makes manipulating data in this way. The focus of this chapter is to bring you up to speed with this essential aspect of our dataviz toolchain.

This chapter is part tutorial, part reference, and sections of it will be referred to in later chapters. If you know the fundamentals of reading and writing Python data, you can cherry-pick parts of the chapter as a refresher.

Easy Does It

I remember when I started programming back in the day (using low-level languages like C) how awkward data manipulation was. Reading from and writing to files was an annoying mixture of boilerplate code, hand-rolled improvisations, and the like. Reading from databases was equally difficult, and as for serializing data, the memories are still painful. Discovering Python was a breath of fresh air. It wasn’t a speed demon, but opening a file was pretty much as simple as it could be:

file = open('data.txt')

Back then, Python made reading from and writing to files refreshingly easy, and its sophisticated string processing made parsing the data in those files just as easy. It even had an amazing module called ...