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# Specifying Thumbnails in `conf.py`

This notebook doesn’t contain a `nbsphinx-thumbnail` cell tag nor cell metadata. Instead, in the file conf.py, a thumbnail is specified (via the nbsphinx_thumbnails option), which will be used in the gallery.

The keys in the `nbsphinx_thumbnails` dictionary can contain wildcards, which behave very similarly to the html_sidebars option.

The thumbnail files can be local image files somewhere in the source directory, but you’ll need to create at least one link to them in order to copy them to the HTML output directory.

You can also use files from the `_static` directory (which contains all files in your html_static_path).

If you want, you can also use files from the `_images` directory, which contains all notebook outputs.

To demonstrate this feature, we are creating an image file here:

    [1]:

    import matplotlib.pyplot as plt

    [2]:

    fig, ax = plt.subplots()
    ax.plot([4, 8, 15, 16, 23, 42])
    fig.savefig('a-local-file.png')
    plt.close()  # avoid plotting the figure

Please note that the previous cell doesn’t have any outputs, but it has generated a file named `a-local-file.png` in the notebook’s directory.

We have to create a link to this file (which is a good idea anyway): a-local-file.png.

Now we can use this file in our conf.py like this:

    nbsphinx_thumbnails = {
        'gallery/thumbnail-from-conf-py': 'gallery/a-local-file.png',
    }

Please note that the notebook name does not contain the `.ipynb` suffix.

Note that the following plot is not used as a thumbnail because the `nbsphinx_thumbnails` setting overrides the default behavior.

    [3]:

    fig, ax = plt.subplots(figsize=[6, 3])
    ax.plot([4, 9, 7, 20, 6, 33, 13, 23, 16, 62, 8], 'r:');