How to Call a Python Script from Scala

Integrating Python scripts with Scala applications can be incredibly useful, especially when leveraging Python’s rich ecosystem of libraries for data science, machine learning, or automation. In this guide, we’ll explore the most popular and efficient way to call a Python script from Scala.

Why Call Python from Scala?

Scala is a powerful JVM-based language, but Python excels in areas like scripting, data analysis, and AI. By combining the two, you can harness the strengths of both languages in a single application.

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Method: Using the ProcessBuilder API

The simplest and most widely used method to call a Python script from Scala is by using Java’s ProcessBuilder API. This approach allows you to execute external processes, including Python scripts, directly from your Scala code.

Step 1: Write a Python Script

First, create a simple Python script (e.g., script.py) that performs a task, such as printing a message or processing data:

# script.py
def main():
    print("Hello from Python!")
    
if __name__ == "__main__":
    main()

Step 2: Call the Script from Scala

In your Scala application, use ProcessBuilder to execute the Python script:

import scala.sys.process._

object PythonFromScala {
  def main(args: Array[String]): Unit = {
    val pythonScriptPath = "path/to/script.py"
    val result = Seq("python3", pythonScriptPath).!!
    println(result) // Output: Hello from Python!
  }
}

Explanation:

• Seq("python3", pythonScriptPath) creates a command sequence to run the script.
• .!! executes the command and captures the output.

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Passing Arguments to Python

You can also pass arguments to your Python script from Scala:

// Scala code
val args = Seq("arg1", "arg2")
val result = Seq("python3", pythonScriptPath) ++ args

In Python, access these arguments using sys.argv:

# Python script
import sys

def main():
    print(f"Received arguments: {sys.argv[1:]}")
    
if __name__ == "__main__":
    main()

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Handling Errors

To handle errors gracefully, use Scala’s Try or Either:

import scala.util.Try

val result = Try(Seq("python3", pythonScriptPath).!!)
result match {
  case Success(output) => println(output)
  case Failure(e) => println(s"Error: ${e.getMessage}")
}

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Alternative: Py4J

For more complex interactions, consider Py4J, a library that enables Python and Java (and thus Scala) to communicate bidirectionally.

Summary: Learn how to seamlessly integrate Python scripts into Scala applications using ProcessBuilder or Py4J. Ideal for data pipelines, automation, and machine learning workflows.

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