Tools of the Trade

1. Tools of the Trade

It 2019 it was estimated1 that, in any given minute, 188 million emails are sent, 55 thousand images are posted to Instagram, and 4.5 million YouTube videos are watched. All of this digital activity generates massive amounts of data, and it’s a data scientist’s job to analyze it. Of course, any data set of moderate size cannot be analyzed with pencil and paper alone; instead, we turn to computers to do the heavy lifting. In this course, we will learn several of the most important computational tools used by working data scientists today: Python, Jupyter notebooks, and the Pandas data science package.

In order to utilize the full power of a computer to run an analysis, we’ll need to know the basics of a good programming language. By far, the most popular2 programming language among data scientists is Python. While other languages tend to be verbose and formal, Python is relatively easy-going. In this course, we’ll learn just enough Python to do interesting things with data.


The type of computer programming done by data scientists is quite different from that done by a software engineer building the latest and greatest word processor. We write code in order to explore data sets in a process that is anything but linear. For instance, given a data set listing the salary of every city employee, our first question is probably: What is the highest salary? We’ll soon see that this can be answered with a short piece of Python code. Next, we might ask who has the highest salary This, too, is answered by a small piece of code. And so on. We ask a question, write some code, and interpret the result. Our next question depends on the answer to the last. We use a computer like it is a very powerful calculator.

Because the type of programming done by data scientists is unique, we use a unique tool to write and run our code: Jupyter notebooks. A Jupyter notebook is a mosaic of code, text, HTML, images, videos and more that can be edited and executed right in the browser. Notebooks are like advanced calculators, in the sense that the user can write a piece of code, run it, and see the result below. Many of the pages in these notes are written as Jupyter Notebooks, and you will be able to click a button to open the notebook and interact with the code on the page (even editing it, if you want).


Python is a powerful general purpose programming language, meaning that it isn’t designed for data science in particular. In fact, Python is popularly used for writing web applications (the behind-the-scenes code that runs Reddit is entirely written in Python). By itself, Python doesn’t come with the functionality that data scientists need. Luckily, Python – like all major programming languages – can be extended by installing packages which provide additional capabilities.

Without a doubt, the most important Python package used by data scientists is pandas. Pandas is an immensely powerful tool for exploring and manipulating large data sets. But with great power comes great complexity. There are several ways to perform even the simplest tasks using Pandas, making it a difficult tool to learn.

For this reason, we have designed a simplified version of pandas, which we are calling babypandas. Babypandas is a subset of pandas, meaning that we have carefully taken some of the pieces of pandas, but left out much of it. We’ll be using babypandas throughout this book. Remember: learning how to use babypandas is actually learning how to use pandas, and all of the code you see in these notes uses the same tools that working data scientists are using every day.