# Code blocks that produce figures

This can be done with notebooks, but it's not easy to make references to figures in notebooks. You can also place the code that produces and saves the figure in a separate `.py` file, and include that in a markdown file. Let's say we want to make a simple sine wave:

1. Place the code of the figure in a `.py` file. In this case, `sinewave.py` produces our figure. The code looks like this:
   
        import numpy as np
        import matplotlib.pyplot as plt

        x = np.linspace(0, 2*np.pi, endpoint=True)
        y = np.sin(x)

        plt.figure()
        plt.plot(x, y)
        plt.title('$y=\sin(x)$')
        plt.xlabel('$x$')
        plt.ylabel('$y$')
        plt.savefig('sinewave.svg')
        
   
> **Warning**
> 
> It is important that the name of the saved figure is **exactly** the same as the name of the Python script that generates it. Otherwise, the figure will not be generated by the Runner.

2. Test your code and make sure that the figure looks good. When you are ready to commit, place your code file in `book/code`.

The book uses a Matplotlib [style sheet](https://matplotlib.org/stable/tutorials/introductory/customizing.html); to see what this looks like on your local machin you will have to run `plt.style.use('../../config/matplotlibrc')` after importing Matplotlib. This should be done outside of the `*.py` file you are creating. Note that the example style sheet path assumes you are working in the `book/code` directory. It is recommended to preserve a list of figures using a notebook in `code_checks`, where there are also working examples. It is not necessary to commit `*.svg` files as these are cleaned when the book is generated.

3. Now include the code file by using the following directives:
   
        ````{toggle}
        ```{eval-rst}
        .. literalinclude:: ../sinewave.py
           :language: python
        ```
        ````
> **Note**
> 
> the outer most directive needs an extra tick mark for nested cases.

4. Include the figure as described above. Remember that figures are saved in the `book/figures` directory. We also use a naming convention of `*_py.svg` for figures generated from code, to easily include them in `.gitignore`, since they are built in the CI/CD pipeline.