SwiftHelloPython

Example for using PythonKit for Swift.

Arguments: <path to directory with Python scripts> <base name of Python script>.

It then uses the function replaceAllAs in the Python script to replace all “a” in the text “Aha” by “x”:

def replaceAllAs(text):
  return text.replace("a", "x")

Crucial calls

As a prerequisite, PythonKit has to be added as a dependency of your Swift package, see the Package.swift file.

Then, in your Swift program:

Import PythonKit:

import PythonKit

Import the Python script, using pythonScripts as the path to directory containing your Python script, and pythonModule as the base name of your Python script:

let sys = Python.import("sys")
sys.path.append(pythonScripts)
let script = try Python.attemptImport(pythonModule)

You should not need to use let sys = Python.import("sys") and sys.path.append(pythonScripts) if your Python script has been installed as part of a package.

Call a function of the Python script:

let changedText = String(script.replaceAllAs(text))

Referencing the Python library

You set the environment variable PYTHON_LIBRARY to reference the according CPython library file, on Linux e.g.:

export PYTHON_LIBRARY=/usr/lib/python3.6/config-3.6m-x86_64-linux-gnu/libpython3.6.so

Use find /usr/lib -name *libpython*.so to search for an appropriate Python library on Linux. On macOS, an according library file has the dylib extension.

You may not need to set this environment variable on macOS. But you might have to set "Enable Hardened Runtime" to "No" in the macOS settings when using a Python version installed by you.

To use a specific Python environment, reference the Python library file inside the environment.

Using UTF-8

When using a Python script via PythonKit, Python might run with some "missing" settings. When you need to read UTF-8 encoded files, you need to:

• set PYTHONIOENCODING: export PYTHONIOENCODING=utf-8 on macOS/Linux,
• add the appropriate argument to some calls, e.g. open(path, 'r', encoding="utf-8") instead of just open(path, 'r').

Concurrent calls of Python functions

Note that CPython has the "global interpreter lock" (GIL), so calling into Python scripts concurrently should not work. The GIL might be removed in future versions of CPython (status: end of 2022).

References

• https://www.tensorflow.org/swift/tutorials/python_interoperability
• https://colab.research.google.com/github/tensorflow/swift/blob/main/docs/site/tutorials/python_interoperability.ipynb

More information

• https://github.com/beeware/Python-Apple-support/blob/main/USAGE.md

Related projects

• https://github.com/pvieito/PythonCodable