title: sub_artifact
---
summary: Creates a sub-artifact of the current one.
---
type: method
---
signature: artifact_name, sources=None, source_obj=None, config_hash=None
---
body:

This method can be used as Python decorator to inform the builder to create
an artifact that is related to the current artifact but locally contained
within it.  For instance this is used to implement the thumbnailing and
similar things.

Each artifact needs at least a name which is what the final file will be
called.  For instance `/demo.css` would place an artifact named `demo.css`
in the root folder.  The `sources` is an optional list of files that indicate
that they are responsible for creating this artifact.  It can be left empty
in which case the artifact just tracks the current file.  The `source_obj`
can optionally point to a source object but for most plugins this will never
be set.

The artifact passed to the function is then the [Artifact :ref](../../artifact/)
object for modification.  Note that the function will not be invoked if the
artifact is already considered up to date.

In addition a `config_hash` can be provided with can be a hash value.  If
provided it can identify the configuration that the artifact was created
from.  If the hash changes the artifact will be rebuilt.  Such a hash
can for instance be generated with [get_structure_hash
:ref](../../../utils/get-structure-hash/).

## Example

```python
import os
from lektor.pluginsystem import Plugin

class IncludeFilePlugin(Plugin):

    def setup_env(self, **extra):
        def get_css(artifact_name='/demo.css'):
            ctx = get_ctx()
            @ctx.sub_artifact(artifact_name)
            def build_stylesheet(artifact):
                with artifact.open('w') as f:
                    f.write('body { background: red; }\n')
            return artifact_name
        self.env.jinja_env.globals['get_demo_css'] = get_css
```

Inside a template it can be used like this:

```html+jinja
<link rel=stylesheet href="{{ get_demo_css()|url }}">
```