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Matplotlib uses a *backend* to render the plot. Some backends are "GUI backends", meaning that they can render into a window that displays on your screen. Others are "non-GUI backends" which can only save the plot into an image file.

Matplotlib doesn't come with any GUI backends except for `TkAgg`, which uses Tkinter to display the window. But if [tkinter is missing](https://software.codidact.com/posts/291791) then this won't work. In these cases, Matplotlib will pre-configure itself to use a plain, non-GUI backend just called `agg`.

You can tell Matplotlib which backend to use by calling `matplotlib.use` before importing `matplotlib.pyplot`:

```
import matplotlib
matplotlib.use('TkAgg') # for the Tkinter backend, for example
import matplotlib.pyplot as plt
```

However, this will fail with an `ImportError` or `ModuleNotFoundError` if the named backend isn't available.

If you don't actually need to show the plot on screen, the `agg` backend works just fine: use `.savefig()` (providing a filename) instead of `.show()`. You [can also](https://matplotlib.org/stable/install/index.html) switch to the `pdf`, `ps` or `svg` backends to write files in those formats, instead of an image file.

Support for many backends can be installed via Pip - for example, `pip install pyqt5` will enable the `Qt5Agg` backend.

<section class="notice is-danger">

However, Tkinter [is special because it's supposed to be part of the standard library](https://software.codidact.com/posts/291791). **Do not try to use Pip to install Tkinter support; it will not work and you will install something that may be useless or even harmful.**
</section>

See also the [Matplotlib documentation for optional dependencies](https://matplotlib.org/stable/install/dependencies.html#optional).