How to Call a Python Script from Ruby

Integrating Python scripts into a Ruby application can be useful when you need to leverage Python’s powerful libraries or existing code. This guide will walk you through the most popular and efficient methods to achieve this.

Method 1: Using the system Command

The simplest way to call a Python script from Ruby is by using Ruby’s built-in system command. This method executes the Python script as a shell command.

# Ruby code to call a Python script
system("python3 path/to/your_script.py")

Pros:

• Easy to implement.
• Works for simple scripts.

Cons:

• Limited interaction between Ruby and Python.
• No direct way to capture Python’s output in Ruby.

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Method 2: Using Open3 for Better Control

Ruby’s Open3 module provides more control over subprocess execution, allowing you to capture output, errors, and exit status.

require 'open3'

stdout, stderr, status = Open3.capture3("python3 path/to/your_script.py")

puts "Output: #{stdout}"
puts "Errors: #{stderr}" unless stderr.empty?

This method is ideal when you need to process the Python script’s output in Ruby.

Passing Arguments to Python

You can pass arguments to the Python script like this:

Open3.capture3("python3 path/to/your_script.py arg1 arg2")

In Python, access these arguments using sys.argv:

import sys
print("Arguments:", sys.argv[1:])  # Outputs ['arg1', 'arg2']

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Method 3: Using PyCall for Direct Integration

For deeper integration, the PyCall gem allows Ruby to call Python functions directly. This is useful when you need to interact with Python libraries like NumPy or Pandas.

Installation

gem install pycall

Example Usage

require 'pycall/import'
include PyCall::Import

pyimport :math

puts math.sqrt(16)  # Outputs 4.0

Pros:

• Direct access to Python functions and libraries.
• No need for subprocess management.

Cons:

• Requires additional setup.
• May not support all Python libraries.

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Method 4: Using JSON for Data Exchange

If your Python script returns structured data, you can use JSON for seamless communication between Ruby and Python.

Python Script (data_processor.py)

import json

data = {"result": "success", "value": 42}
print(json.dumps(data))

Ruby Code

require 'json'

output = `python3 data_processor.py`
parsed_data = JSON.parse(output)

puts parsed_data["result"]  # Outputs "success"

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Summary: Calling Python from Ruby can be done via system, Open3, PyCall, or JSON-based data exchange. Choose the method based on your needs—simple execution, output handling, or deep integration.

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