Getting Started with ScalaPy

ScalaPy makes it easy to use Python libraries from Scala code. With a simple API, automatic conversion between Scala and Python types, and optional static typing, ScalaPy scales from hobby projects to production systems.

Installation

First, add ScalaPy to your SBT build:

// JVM

libraryDependencies += "me.shadaj" %% "scalapy-core" % "0.4.2"

// Scala Native

libraryDependencies += "me.shadaj" %%% "scalapy-core" % "0.4.2"

You'll then need to add the Python native libraries to your project and configure SBT to run your code in a separate JVM instance.

fork := true

import scala.sys.process._

lazy val pythonLdFlags = {

val withoutEmbed = "python3-config --ldflags".!!

if (withoutEmbed.contains("-lpython")) {

withoutEmbed.split(' ').map(_.trim).filter(_.nonEmpty).toSeq

} else {

val withEmbed = "python3-config --ldflags --embed".!!

withEmbed.split(' ').map(_.trim).filter(_.nonEmpty).toSeq

}

}

lazy val pythonLibsDir = {

pythonLdFlags.find(_.startsWith("-L")).get.drop("-L".length)

}

javaOptions += s"-Djna.library.path=$pythonLibsDir"

If you'd like to use Scala Native, follow the instructions there to create a project with Scala Native 0.4.0-M2. Then, add the following additional configuration to your SBT build to link the Python interpreter.

lazy val pythonLdFlags = ... // same as above

nativeLinkingOptions ++= pythonLdFlags

Hello World!

Now that ScalaPy is installed, let's start with a simple example. ScalaPy offers a dynamically typed API that's great for making quick Python calls with little ceremony. First, we can use the Python len function to calculate the length of a list. Using py.Dynamic.global, you can access any members of the global scope.

import me.shadaj.scalapy.py

import me.shadaj.scalapy.py.SeqConverters

val listLengthPython = py.Dynamic.global.len(List(1, 2, 3).toPythonProxy)

// listLengthPython: py.Dynamic = 3

Here, we took a Scala List, converted it to a Python list, sent it to the len function, and got back a Python number.

To convert Python values back into Scala, we use the .as method and pass in the type we want.

val listLength = listLengthPython.as[Int]

// listLength: Int = 3

Execution

ScalaPy officially supports Python 3.{7, 8, 9}. If you want to use another version of Python, you should define the environment variable SCALAPY_PYTHON_LIBRARY

python --version

# Python 3.8.6

export SCALAPY_PYTHON_LIBRARY=python3.8

sbt run