Python Polars: The Definitive Guide

Chapter 6. Reading and Writing Data

Now that you’ve seen some essential concepts such as data types and the different APIs, you’re ready to learn about working with external data sources. That includes reading data from files and databases into Polars. We’ll also cover how to write your results to files and databases. By the end of this chapter, you’ll be able to start working with your own data. We encourage you to start using your own data as soon as possible, because it will make learning about Polars not only more enjoyable but also more effective.

External data can come in all sorts of ways from all sorts of places. Because of this, Polars has over 30 functions related to reading data, and those functions accept many arguments. It would be challenging and, more importantly, extremely boring to cover every function and every argument in this chapter. That’s what the official API documentation is for. We’ll give a quick overview of the formats Polars supports, together with the relevant methods to work with them. In the rest of the chapter, we will focus on the formats and situations that you’re most likely to encounter.

In this chapter, you’ll learn how to:

• Read and write data in many formats, including CSV, Excel, and Parquet

• Handle multiple files efficiently using globbing

• Correctly read missing values

• Deal with character encodings

• Read data eagerly and lazily

You’ll be using a couple of additional packages:

• xlsx2csv to read Excel spreadsheets

• chardet to ...