HowToLens Lectures

The best way to learn PyAutoLens is by going through the HowToLens lecture series on the autolens workspace.

The lectures are provided as Jupyter notebooks (and Python scripts), and they are linked to via this readthedocs. The lectures are composed of five chapters

  • Introduction - An introduction to strong gravitational lensing and PyAutolens.
  • Lens Modeling - How to model strong lenses, including a primer on Bayesian non-linear analysis.
  • Search Chaining - How to fit complex lens models using non-linear search chaining.
  • LinearEqns - How to perform pixelized reconstructions of the source-galaxy.
  • Hyper-Mode - How to use PyAutoLens advanced modeling features that adapt the model to the strong lens being analysed.

How to Tackle HowToLens

The HowToLens lecture series currently sits at 5 chapters, and each will take around 3-6 hours to go through thoroughly. You probably want to be modeling lenses with PyAutoLens faster than that! Furthermore, the concepts in the later chapters are pretty challenging, and familiarity with PyAutoLens and lens modeling is desirable before you tackle them.

Therefore, we recommend that you complete chapters 1 & 2 and then apply what you’ve learnt to the modeling of simulated and real strong lenses imaging, using the scripts found in the ‘autolens_workspace’ modeling packages. Once you’re confident with your use of PyAutoLens, you can then begin to cover the advanced functionality covered in chapters 3, 4 & 5.

Lensing Theory

HowToLens assumes minimal previous knowledge of gravitational lensing and astronomy. However, it is beneficial to give yourself a basic theoretical grounding as you go through the lectures. I heartily recommend you have open the lecture course on gravitational lensing by Massimo Meneghetti below as you go through the tutorials, and refer to it for anything that isn’t clear in HowToLens.


Before beginning the HowToLens lecture series, in chapter 1 you should do ‘tutorial_0_visualization’. This will take you through how PyAutoLens interfaces with matplotlib to perform visualization and will get you setup such that images and figures display correctly in your Jupyter notebooks.

Jupyter Notebooks

The tutorials are supplied as Jupyter Notebooks, which come with a ‘.ipynb’ suffix. For those new to Python, Jupyter Notebooks are a different way to write, view and use Python code. Compared to the traditional Python scripts, they allow:

  • Small blocks of code to be viewed and run at a time
  • Images and visualization from a code to be displayed directly underneath it.
  • Text script to appear between the blocks of code.

This makes them an ideal way for us to present the HowToFit lecture series, therefore I recommend you get yourself a Jupyter notebook viewer ( if you havent done so already.

If you really want to use Python scripts, all tutorials are supplied a .py python files in the ‘scripts’ folder of the workspace.

Code Style and Formatting

You may notice the style and formatting of our Python code looks different to what you are used to. For example, it is common for brackets to be placed on their own line at the end of function calls, the inputs of a function or class may be listed over many separate lines and the code in general takes up a lot more space then you are used to.

This is intentional, because we believe it makes the cleanest, most readable code possible. In fact, lots of people do, which is why we use an auto-formatter to produce the code in a standardized format. If you’re interested in the style and would like to adapt it to your own code, check out the Python auto-code formatter ‘black’.