Embedding Build Tools

The GraalPy Maven and Gradle plugins provide functionality to manage Python related resources required for embedding Python code in Java-based applications:

Python application files provided by the user, for example, Python sources which are part of the project.
Third-party Python packages installed by the plugin during the build according to the plugin configuration.
The Python standard library, which is necessary to make Native Image generated executables self-contained.

Apart from physically managing and deploying those files, it is also necessary to make them available in Python at runtime by configuring the GraalPy Context in your Java code accordingly. The GraalPyResources API provides factory methods to create a Context preconfigured for accessing Python, embedding relevant resources with a Virtual Filesystem or from a dedicated external directory.

Deployment #

There are two modes how to deploy the resources: as Java resources using the Virtual Filesystem to access them in Python, or as an external directory.

Virtual Filesystem #

The Python related resources are embedded in the application file, either in JAR or Native Image generated executable, as standard Java resources. The GraalPy Virtual Filesystem accesses resource files as standard Java resources and makes them available to Python code running in GraalPy. This is transparent to the Python code, which can use standard Python IO to access those files.

Java resource files in a Maven or Gradle project are typically located in dedicated resources directories. All resources subdirectories named org.graalvm.python.vfs are merged and mapped to a configurable Virtual Filesystem mount point at the Python side, by default /graalpy_vfs. For example, a Python file with the real filesystem path ${project_resources_directory}/org.graalvm.python.vfs/src/foo/bar.py will be accessible as /graalpy_vfs/src/foo/bar.py in Python.

Use the following GraalPyResources factory methods to create GraalPy Context preconfigured for the use of the Virtual Filesystem:

GraalPyResources.createContext()
GraalPyResources.contextBuilder()
GraalPyResources.contextBuilder(VirtualFileSystem)

External Directory #

As an alternative to Java resources with the Virtual Filesystem, it is also possible to configure the Maven or Gradle plugin to manage the contents of an external directory, which will not be embedded as a Java resource into the resulting application. A user is then responsible for the deployment of such directory. Python code will access the files directly from the real filesystem.

Use the following GraalPyResources factory methods to create GraalPy Context preconfigured for the use of an external directory:

GraalPyResources.createContextBuilder(Path)

Conventions #

The factory methods in GraalPyResources rely on the following conventions, where the ${root} is either an external directory, or a Virtual System mount point on the Python side and ${project_resources_directory}/org.graalvm.python.vfs on the real filesystem:

${root}/src: used for Python application files. This directory will be configured as the default search path for Python module files (equivalent to PYTHONPATH environment variable).
${root}/venv: used for the Python virtual environment holding installed third-party Python packages. The Context will be configured as if it is executed from this virtual environment. Notably packages installed in this virtual environment will be automatically available for importing.
${root}/home: used for the Python standard library (equivalent to PYTHONHOME environment variable).

The Maven or Gradle plugin will fully manage the contents of the venv and home subdirectories. Any manual changes in these directories will be overridden by the plugin during the build.

${root}/venv: the plugin creates a virtual environment and installs required packages according to the plugin configuration in pom.xml or build.gradle.
${root}/home: the plugin copies the required (also configurable) parts of the Python standard library into this directory. By default, the full standard library is used.

The src subdirectory is left to be manually populated by the user with custom Python scripts or modules.

GraalPy Maven Plugin Configuration #

Add the plugin configuration in the configuration block of graalpy-maven-plugin in the pom.xml file:

<plugin>
    <groupId>org.graalvm.python</groupId>
    <artifactId>graalpy-maven-plugin</artifactId>
    ...
    <configuration>
        ...
    </configuration>
    ...
</plugin>

The packages element declares a list of third-party Python packages to be downloaded and installed by the plugin.

The Python packages and their versions are specified as if used with pip:

<configuration>
    <packages>
        <package>termcolor==2.2</package>
        ...
    </packages>
    ...
</configuration>

The pythonHome subsection declares what parts of the standard library should be deployed.

Each include and exclude element is interpreted as a Java-like regular expression specifying which file paths should be included or excluded.

<configuration>
    <pythonHome>
        <includes>
            <include>.*</include>
            ...
        </includes>
        <excludes>
            <exclude></exclude>
            ...
        </excludes>
    </pythonHome>
    ...
</configuration>

If the pythonResourcesDirectory element is specified, then the given directory is used as an external directory and no Java resources are embedded. Remember to use the appropriate GraalPyResources API to create the Context.
```
<configuration>
    <pythonResourcesDirectory>${basedir}/python-resources</pythonResourcesDirectory>
    ...
</configuration>
```

GraalPy Gradle Plugin Configuration #

Add the plugin configuration in the GraalPy block in the build.gradle file. The packages element declares a list of third-party Python packages to be downloaded and installed by the plugin.

The Python packages and their versions are specified as if used with pip.
```
graalPy {
  packages = ["termcolor==2.2"]
  ...
}
```
The pythonHome subsection declares what parts of the standard library should be deployed.

Each element in the includes and excludes list is interpreted as a Java-like regular expression specifying which file paths should be included or excluded.
```
graalPy {
  pythonHome {
    includes = [".*"]
    excludes = []
  }
  ...
}
```
If the pythonResourcesDirectory element is specified, then the given directory is used as an external directory and no Java resources are embedded. Remember to use the appropriate GraalPyResources API to create the Context.
```
graalPy {
  pythonResourcesDirectory = file("$rootDir/python-resources")
  ...
}
```