# How to structure your Python scripts for Sphinx-Gallery

This page describes the structure and syntax that can be used in Python scripts to generate rendered HTML gallery pages.

## A simple example

Sphinx-Gallery expects each Python file to have two things:

1. A docstring, written in rST, that defines the header for the example. It must begin by defining a rST title. The title may contain any punctuation mark but cannot start with the same punctuation mark repeated more than 3 times. For example:

       """
       "This" is my example-script
       ===========================

       This example doesn't do much, it just makes a simple plot
       """

2. Python code. This can be any valid Python code that you wish. Any Matplotlib images that are generated will be saved to disk, and the rST generated will display these images with the built examples. By default only images generated by Matplotlib, or packages based on Matplotlib (e.g., Seaborn or Yellowbrick) are saved and displayed. However, you can change this to include other packages, see Image scrapers.

For a quick reference have a look at the example Introductory example - Plotting sin

## Embed rST in your example Python files

Additionally, you may embed rST syntax within your Python scripts. rST allows you to easily add formatted text, math equations and reference links, including cross referencing other examples. This will be rendered in-line with the Python code and its outputs, similar to how Jupyter Notebooks are structured (in fact, Sphinx-Gallery also creates a Jupyter Notebook for each example that is built).

You can embed rST in your Python examples by including a line of >= 20 `#` symbols, `#%%`, or `# %%`. For consistency, it is recommended that you use only one of the above three ‘block splitter’ options in your project. If using a line of `#`’s, we recommend using 79 `#`’s, like this:

    ###############################################################################

Any commented lines (line beginning with `#` followed by a space, to be PEP8-compliant) that immediately follow a block splitter will be rendered as rST in the built gallery examples. To switch back to writing code, either stop starting lines with `#` and a space or leave an empty line before writing code comments. You can thus easily alternate between text and code ‘blocks’. For example:

    # This is commented python
    myvariable = 2
    print("my variable is {}".format(myvariable))

    # %%
    # This is a section header
    # ------------------------
    #
    # In the built documentation, it will be rendered as rST. All rST lines
    # must begin with '# ' (note the space) including underlines below section
    # headers.

    # These lines won't be rendered as rST because there is a gap after the last
    # commented rST block. Instead, they'll resolve as regular Python comments.
    # Normal Python code can follow these comments.
    print('my variable plus 2 is {}'.format(myvariable + 2))

The `#%%` and `# %%` syntax is consistent with the ‘code block’ (or ‘code cell’) separator syntax in Visual Studio Code Python extension, Visual Studio Python Tools, Jupytext, Pycharm Professional, Hydrogen plugin (for Atom) and Spyder. Note that although the documentation of these editors/IDEs may only mention one of `#%%` or `# %%`, in practice both work. With these editors/IDEs, `#%%` or `# %%` at the start of a line signifies the start of a new code block. Code blocks allow you to separate your code into chunks, like in Jupyter Notebooks. All the code within a code block can be easily executed together. This functionality can be helpful when writing a Sphinx-Gallery `.py` example as the blocks allow you to easily create pairs of subsequent Sphinx-Gallery text and code blocks.

Here are the contents of an example Python file using the ‘code block’ functionality:

    """
    This is my example script
    =========================

    This example doesn't do much, it just makes a simple plot
    """

    # %%
    # This is a section header
    # ------------------------
    # This is the first section!
    # The `#%%` signifies to Sphinx-Gallery that this text should be rendered as
    # rST and if using one of the above IDE/plugin's, also signifies the start of a
    # 'code block'.

    # This line won't be rendered as rST because there's a space after the last block.
    myvariable = 2
    print("my variable is {}".format(myvariable))
    # This is the end of the 'code block' (if using an above IDE). All code within
    # this block can be easily executed all at once.

    # %%
    # This is another section header
    # ------------------------------
    #
    # In the built documentation, it will be rendered as rST after the code above!
    # This is also another code block.

    print('my variable plus 2 is {}'.format(myvariable + 2))

For a clear example refer to the rendered example Alternating text and code and compare it to the generated `original python script`