How to Call a Python Script from Swift

Integrating Python scripts with Swift can be a powerful way to leverage Python’s extensive libraries while building native iOS or macOS applications. Whether you're processing data, running machine learning models, or automating tasks, calling Python from Swift is simpler than you might think.

Prerequisites

Before diving in, ensure you have the following:

Xcode installed (for Swift development).
Python installed on your system (preferably Python 3.7+).
Basic familiarity with Swift and Python scripting.

Method 1: Using PythonKit

PythonKit is a popular Swift library that allows seamless integration with Python. It provides a bridge between Swift and Python, enabling direct execution of Python code.

Step 1: Install PythonKit

Add PythonKit to your Swift project using Swift Package Manager (SPM). Open your Package.swift file and add the dependency:

dependencies: [
    .package(url: "https://github.com/pvieito/PythonKit.git", from: "0.3.0")
]

Step 2: Import and Use PythonKit

In your Swift file, import PythonKit and execute Python code:

import PythonKit

let sys = Python.import("sys")
print("Python Version: \(sys.version)")

// Call a Python function
let math = Python.import("math")
let result = math.sqrt(25)
print("Square root of 25 is \(result)")

Method 2: Running Python Scripts via Process API

If you prefer running an external Python script, Swift’s Process API can execute shell commands.

Step 1: Prepare Your Python Script

Save a Python script (e.g., script.py) with a function:

# script.py
def greet(name):
    return f"Hello, {name}!"

if __name__ == "__main__":
    import sys
    print(greet(sys.argv[1]))

Step 2: Execute the Script from Swift

Use Process to run the script and capture output:

import Foundation

let process = Process()
process.executableURL = URL(fileURLWithPath: "/usr/bin/python3")
process.arguments = ["/path/to/script.py", "Swift"]

let pipe = Pipe()
process.standardOutput = pipe

try process.run()
process.waitUntilExit()

let data = pipe.fileHandleForReading.readDataToEndOfFile()
if let output = String(data: data, encoding: .utf8) {
    print(output.trimmingCharacters(in: .whitespacesAndNewlines))
}

Best Practices

Error Handling: Always handle exceptions in Python and Swift to avoid crashes.
Performance: For heavy computations, consider running Python scripts in the background.
Security: Avoid passing untrusted input to Python scripts.

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