Overview

Java code that shows how to call python with graalvm, and the different ways of passing and receiving objects, from Java to Python and from Python to Java.

Requirements

• SDK Man
• Install the graalvm sdk install java 20.0.0.r11-grl
• Set graalvm as the current java sdk use java 20.0.0.r11-grl
• Install the graalvm python libraries gu install python
• Test by running graalpython

Use cases

Java to Python and back

Maps and Lists

Maps, Arrays and Lists need to be wrapped in a ProxyObject or ProxyArray interface to be use-able in Python as native objects arrays and lists.

Create a Java object and call methods on it from Python

then returning a Java class from Python to Java.

The object must be available in the bindings. And if allowAllAccess or allowHostAccess is set with true on the context Python can call methods and send arguments to the Java objects.

Create a Java object from Python

Via Bindings

The class name must be set to the bindings and as a class.
For example binginds("Person", Person.class), now you can run Person('name', 21) and python will create the Java Person class.

Via import type

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import java
Person = java.type('gerrit.graalvm.java2py.Person')
Person('Jack', 21)

Python to Java and back

Maps and Lists

Python lists can be cast to the Collection, List, Iterable Java interfaces.

Python dictionaries can be cast to the Map Java interface.

Gets work as expected, but keySet does not, and returns the truffle object proxy methods.

Create a Python Object, return it to Java and functions on it

From Python:

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class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age
                  
p = Person('Jack', 30)
p

From Java:

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Value pyPerson = eval(...);

System.out.println("pyPerson getMember(name): " + pyPerson.getMember("name"));
//pyPerson getMember(name): 'Jack'

pyPerson.putMember("age", 22);
System.out.println("pyPerson getMember(age): " + pyPerson.getMember("age"));
//pyPerson getMember(age): 22