Tutorial, Step 1: Setup

Prerequisites

In order to work with Great Expectations, you will need:

• A working Python install (3.7 to 3.10)
• The ability to pip install for Python
  • Note: A best practice would be to do this in a virtual environment!
• A working Git install
• A working internet browser install (for viewing Data Docs in steps 3 and 4).

If you need assistance with setting up any of these utilities, we have links to their documentation on our page for supporting resourcesA resource external to the Great Expectations code base which Great Expectations utilizes..

Setting up the tutorial data

The first thing we'll need is a copy of the data that this tutorial will work with. Fortunately, we've already put that data into a convenient repository that you can clone to your machine.

Clone the gx_tutorials repository to download the data. This repository also contains directories with the final versions of the tutorial, which you can use for reference.

To clone the repository and go into the directory you'll be working from, start from your working directory and enter the following commands into your terminal:

git clone https://github.com/great-expectations/gx_tutorials
cd gx_tutorials

The repository you cloned contains several directories with final versions for this and our other tutorials. The final version for this tutorial is located in the getting_started_tutorial_final_v3_api folder. You can use the final version as a reference or to explore a complete deployment of Great Expectations, but you do not need it for this tutorial.

Install Great Expectations and dependencies

Great Expectations requires Python 3 and can be installed using pip. If you haven’t already, install Great Expectations by running:

pip install great_expectations

You can confirm that installation worked by running

great_expectations --version

This should return something like:

great_expectations, version 0.15.49

For detailed installation instructions, see How to install Great Expectations locally.

Other deployment patterns

This tutorial deploys Great Expectations locally. Note that other options (e.g. running Great Expectations on an EMR Cluster) are also available. You can find more information in the Reference Architectures section of the documentation.

Create a Data Context

In Great Expectations, your Data ContextThe primary entry point for a Great Expectations deployment, with configurations and methods for all supporting components. manages your project configuration, so let’s go and create a Data Context for our tutorial project!

When you installed Great Expectations, you also installed the Great Expectations command line interface (CLICommand Line Interface). It provides helpful utilities for deploying and configuring Data Contexts, plus a few other convenience methods.

To initialize your Great Expectations deployment for the project, run this command in the terminal from the gx_tutorials directory:

great_expectations init

You should see this:

Using v3 (Batch Request) API

  ___              _     ___                  _        _   _
 / __|_ _ ___ __ _| |_  | __|_ ___ __  ___ __| |_ __ _| |_(_)___ _ _  ___
| (_ | '_/ -_) _` |  _| | _|\ \ / '_ \/ -_) _|  _/ _` |  _| / _ \ ' \(_-<
 \___|_| \___\__,_|\__| |___/_\_\ .__/\___\__|\__\__,_|\__|_\___/_||_/__/
                                |_|
             ~ Always know what to expect from your data ~

Let's create a new Data Context to hold your project configuration.

Great Expectations will create a new directory with the following structure:

    great_expectations
    |-- great_expectations.yml
    |-- expectations
    |-- checkpoints
    |-- plugins
    |-- .gitignore
    |-- uncommitted
        |-- config_variables.yml
        |-- data_docs
        |-- validations

OK to proceed? [Y/n]: <press Enter>

When you see the prompt, press enter to continue. Great Expectations will build out the directory structure and configuration files it needs for you to proceed. All of these together are your Data Context.

note

Your Data Context will contain the entirety of your Great Expectations project. It is also the entry point for accessing all of the primary methods for creating elements of your project, configuring those elements, and working with the metadata for your project. That is why the first thing you do when working with Great Expectations is to initialize a Data Context!

You can follow this link to read more about Data Contexts.

About the great_expectations directory structure

After running the init command, your great_expectations directory will contain all of the important components of a local Great Expectations deployment. This is what the directory structure looks like

• great_expectations.yml contains the main configuration of your deployment.

• The expectations directory stores all your ExpectationsA verifiable assertion about data. as JSON files. If you want to store them somewhere else, you can change that later.

• The plugins/ directory holds code for any custom plugins you develop as part of your deployment.
• The uncommitted/ directory contains files that shouldn’t live in version control. It has a .gitignore configured to exclude all its contents from version control. The main contents of the directory are:
  • uncommitted/config_variables.yml, which holds sensitive information, such as database credentials and other secrets.
  • uncommitted/data_docs, which contains Data Docs generated from Expectations, Validation Results, and other metadata.
  • uncommitted/validations, which holds Validation Results generated by Great Expectations.

Congratulations, that's all there is to Step 1: Setup with Great Expectations. You've finished the first step! Let's move on to Step 2: Connect to Data