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Jupyter Notebooks and Tutorials

Jupyter Notebooks are a convenient format for creating and sharing documents that combine code, data analyses, visualizations, and prose, which are the key components of a tutorial. This guide describes best practices for creating readable (easy to understand) and portable (likely to work on many computers) notebooks. Following this guide is a requirement for those authors contributing content to the STScI notebooks repository. This style guide, when not documenting notebook-specific syntax, also applies to other formats like non-notebook tutorials or example descriptions.

Example notebook

This example notebook provides a tutorial template with placeholder content based on this style guide. If you want to create a new tutorial following this guide, then you might want to start from this example notebook.

Design principles

Make no assumptions

As the tutorial author, don't assume people know the same things as you. This means that any terms or common acronyms should be defined when they are first used. It you're using some kind of astronomical parameter, make sure you define it (for example, in its mathematical form) or link to any definitions (literature, Wikipedia, etc.). If you think this information is making your tutorial too detailed, use clearly named sections with appropriate introductions, or split your tutorial into two separate tutorials that reference each other.

Above all, know your audience: if you are writing a tutorial for astronomers in a specific field, you might be more terse on background. But if so, say so at the beginning of your tutorial, and know that most readers will not get anything from it.

Always avoid assumptive or belittling words such as “obviously,” “easily,” “simply,” “just,” or “straightforward.” Avoid words or phrases that create worry in the mind of the reader. Instead, use positive language that establishes confidence in the skills being learned.

Design for portability

Tutorials should be portable, that is, they should be designed to work on multiple computers. There are a few basic steps you can take as a tutorial author to increase the "portability" of a tutorial notebook:

  • Use APIs, not file systems, to access data. Where possible, use libraries such as astroquery.mast to retrieve the data required for your notebook. Never hard-code a path to a file on, for example, a shared filesystem. See the data guide for more detail on how you might implement this.
  • If you need specific packages installed to enable your notebook to execute, define them in a custom requirements.txt file that can be used to install these dependencies. Be as specific as possible: sometimes packages make backward incompatible changes, so specifying a particular version of dependencies will protect against that.
  • Try to avoid long-running computations or large downloads. Not all users will have good internet access or a fast computer when they try to run your notebook. Instead, try to use compact examples that work on smaller portions of a dataset. While this is not always possible given the goals of a particular tutorial, it is best to strive for it. At the very least, be sure to warn the user clearly if a notebook will have long runtime or large downloads.
  • Avoid using any unnecessary non-markdown constructs. While it's tempting to use HTML directly in a notebook cell, it's best avoided if at all possible, because there's no guarantee that the notebook viewer is in the same website all the time. Markdown, meanwhile, is specifically designed with that portability in mind.

Keep good cell discipline

A notebook cell

Creating a new tutorial can take time, and in the development process, some content cells (code and prose) may become out of date or superfluous. Before committing your work to a source repository, make sure that:

  • Cells capture logical units of work. That is, don't put all of your code in a single giant cell of logic. Try to break it out into smaller units, interspersed with text explaining what you are doing.
  • All of the cells are required and in order. That is, you can go from the start of your notebook to the end, executing each cell. Cells should only fail if they are meant to, because you're illustrating the meaning of an error message or something similar.
  • Checked-in notebooks shouldn't contain the executed cell outputs. Any results you check in take up valuable space in the notebook, making it harder to review and bloating the repository. When your notebook is checked into the STScI notebooks repository, we will run nbconvert to execute your notebook (overriding anything already executed) and sphinx to create web-hosted versions.

Write readable prose using Markdown

Use cells with Markdown formatting to describe anything that isn't actually code. Also use them either before or after code cells to describe what's happening. When mathematical expressions are needed, use the Jupyter additions to Markdown, which are basically carefully controlled LaTeX.

Only use code comments when it's a natural inline comment directly connected to that line of code. Do not use code cells with comments to replace well-written prose!

On-disk layout and ancillary/generated files

Individual notebooks should live in their own directory alongside any ancillary files related to them. For example:

notebooks/
|-- MyAwesomeNotebook
|    |-- my_awesome_notebook.ipynb
|    +-- object-data.csv
|    +-- result-plot.png
|    +-- requirements.txt

As this demonstrates, sometimes it is appropriate to include ancillary files with your notebook. Examples include small images or data files such as FITS cutouts not accessible via MAST, or CSV tables. Files of any significant size (> 100 kB is a good rule of thumb) should not be included with the notebook but rather stored outside of the repository and accessed via code (go to the data guide for details on how to do this). As shown previously, if your notebook needs ancillary files, you should include them at the same level as your notebook.

Similarly, if your tutorial involves writing files, you should write the notebook so that they are written in the same location. As an example, if you are making a scatter plot using matplotlib and want to demonstrate to the user how to save it, you can do this in the notebook:

plt.scatter(...)
plt.savefig('result-plot.png')

And the image will end up in the same place as any ancillary files.

Recommended tutorial structure

It's recommended that tutorials use the following suggested structure:

Title

Pick a clear, descriptive title. For titles, use title case capitalization and the following Markdown syntax:

# My Clear, Descriptive Title

Learning Goals

Every tutorial should contain three to five explicit learning goals. A learning goal should describe what a reader should know or be able to do by the end of the tutorial that they didn't know or couldn't do before.

Learning goals can be broken down into:

  • Skills: what the reader should be able to do by the end of the tutorial.
  • Knowledge: what the reader should understand by the end of the tutorial.
  • Attitudes: what the reader's opinions about the subject matter will be by the end of the tutorial.

To create your tutorial learning goals, write sentences that identify what skill, knowledge, or attitude the reader will gain from your tutorial, and use strong action verbs (understand, explain, demonstrate, determine, create, access, calculate, analyze).

Template learning goal sentence:

By the end of this tutorial, you will be able to (skill) in order to (knowledge).

Examples

By the end of this tutorial, you will:

- Understand how to use aperture photometry to turn a series of two-dimensional
  images into a one-dimensional time series.
- Be able to determine the most useful aperture for photometry on a *Kepler/K2*
  target.
- Create your own light curve for a single quarter/campaign of *Kepler/K2* data.

By the end of this tutorial, you will be able to:

- Understand how NASA's Kepler Mission collected and released light curve data
  products.
- Download and plot light curve files from the data archive using `Lightkurve`.
- Access light curve metadata.
- Understand the time and brightness units.

Introduction

Write a short introduction explaining the purpose of the tutorial. Define any terms or common acronyms that your audience may not know. If you're using some kind of domain-specific astronomical symbol or unusual mathematical concept, make sure you define it (for example, in its mathematical form) and link to any definitions (from literature, Wikipedia, etc.).

If there are background materials or resources that may be useful to the reader to provide additional context, you may link to it here. If your tutorial is a continuation from another tutorial, or there are other tutorials that would be useful for the reader to read before or after your tutorial, mention that here as well.

Imports

Import your dependencies after the introduction and explain why you're including each one. For example:

Imports

Main Content

The main content of your tutorial should be subdivided into numbered sections with useful, descriptive headings that make sense based on the content. Break sections up with standard Markdown syntax headings:

## Section 1

Intro to Section 1

### Subsection 1a

More detailed info about Section 1

## Section 2

A complete thought that's as important as Section 1 but doesn't need
subsections.

Be sure to use the Markdown headings (that is, the number of #'s) in a way that gives hierarchical meaning to your tutorial. The heading levels are used to do things like intelligently make links and the Table of Contents, so you don't want to confuse things by using heading levels that don't match the logical flow of the tutorial.

Loading data and file information should appear within your main content, at the same time the data is going to be used, if possible. These elements of your tutorial can be their own sections within the main content, but avoid generic or vague headings like “Loading Data” and instead use descriptive headings pertinent to the content of the tutorial and the actual data being downloaded or files being used. For example, instead of a vague heading like "Downloading Data," use something like “Downloading Multiple KeplerLightCurve Objects at Once.” For additional details on loading data and file information, read the following sections.

Loading Data

If the user needs to download data to run the tutorial properly, where possible, use Astroquery (or similar) to retrieve files. If this is not possible, see the data guide for other options.

File Information

Explain pertinent details about the file you've just downloaded. For example, if working with Kepler light curves, explain what's in the different file extensions:

- No. 0 (Primary): This HDU contains metadata related to the entire file.
- No. 1 (Light curve): This HDU contains a binary table that holds data like
  flux measurements and times. We will extract information from here when we
  define the parameters for the light curve plot.
- No. 2 (Aperture): This HDU contains the image extension with data collected
  from the aperture. We will also use this to display a bitmask plot that
  visually represents the optimal aperture used to create the SAP_FLUX column in
  HDU1.

Where possible (if the code supports it), use code examples that visually display the data in the tutorial. For example, if you are showing an object that can be read as an Astropy table, display the table:

show-data-example

Terms and Resources

All terms and relevant additional resources should be defined and linked to as new topics are introduced and your tutorial progresses, so that terms and resources appear within the context of your main content. Short exercises can be woven into your main content sections as well.

Exercises

Exercises are optional, but encouraged. Exercises can be woven into the main content of your tutorial, or appear in their own section toward the end of the tutorial. Final exercises can be more challenging, similar to homework problems. They can be minimal or take as long as 30 minutes to an hour to complete.

Most tutorials convey information to their reader by posing questions and then providing answers. But as so many of us learn by doing, it's encouraged for you to provide exercises in your tutorial that pose questions but do not include immediate answers so that your reader can practice their new skills to cement the knowledge in their minds.

If you do have one or more exercises, be sure to leave a blank code cell underneath each to show the reader that they're meant to try out their new skill right there. You may also want to include a "solutions" notebook next to your main notebook for the reader to check their work after they have finished their attempt.

Additional Resources

This section is optional. Try to weave resource links into the main content of your tutorial so that they are falling in line with the context of your writing. For resources that do not fit cleanly into your narrative, you may include an additional resources section at the end of your tutorial. Usually a list of links using Markdown bullet list plus link format is appropriate:

* [A neat resource to learn
  more](http://learning.org/how-i-learned-science-is-cool.html)
* [A place to find more relevant code](https://github.com/spacetelescope/jwst)

About this Notebook

Let the world know who the author of this great tutorial is! If possible and appropriate, include a contact email address for users who might need support (for example, archive@stsci.edu). You can also optionally include keywords, your funding source, or a last update date in this section.

Citations

Provide your reader with guidelines on how to cite open source software and other resources in their own published work.

Example

If you use `astropy` or `lightkurve` for published research, please cite the
authors. Follow these links for more information about citing `astropy` and
`lightkurve`:

* [Citing `astropy`](https://www.astropy.org/acknowledging.html)
* [Citing `lightkurve`](http://docs.lightkurve.org/about/citing.html)

Footer

Notebooks should use the standard STScI footer:

Footer

This can be implemented with the following code snippet placed in a cell at the bottom of the notebook.

<img style="float: right;" src="https://raw.githubusercontent.com/spacetelescope/notebooks/master/assets/stsci_pri_combo_mark_horizonal_white_bkgd.png" alt="Space Telescope Logo" width="200px"/>

The example notebook implements the footer in this way.

Further reading

STScI follows The Chicago Manual of Style and the Merriam-Webster Dictionary. STScI writing guidelines are in agreement with the Astropy Narrative Style Guide.

Example tutorials following this style guide

Here are some example tutorials that follow this style guide:

Other Resources

For a related view of tutorial styles in the astronomy context, see the Astropy Contributing Guide.

Contributing to the STScI notebooks repository

View the contributing guide in the STScI notebooks repository.