How to install PyCall with a specific Python version?

Set the PYTHON environment variable to the path of the python executable before installing the gem. For pyenv, ensure Python is built with --enable-shared to provide the required shared library.

PyCall vs RubyPython or other bridges: which is better?

PyCall offers more Ruby-idiomatic syntax and automatic type conversion, while alternatives like RubyPython may differ in performance and maintenance. PyCall is actively maintained with red-data-tools extensions, but benchmark for your use case.

Does PyCall work with TensorFlow or scikit-learn?

Yes, you can import these libraries directly, but for optimal performance with numpy or pandas, use the dedicated red-data-tools wrappers mentioned in the README to avoid potential issues.

How to debug PyCall when it can't find Python?

Set PYCALL_DEBUG_FIND_LIBPYTHON=1 to enable detailed logging of the library search process, helping identify missing shared libraries or incorrect Python paths.

Can I use PyCall in a Rails app on Heroku?

Yes, but you must add the Python buildpack first, specify Python version in .python-version and dependencies in requirements.txt, as detailed in the deployment section, to ensure proper environment setup.

What are the performance costs of using PyCall?

Automatic type conversion and GIL management introduce overhead; for high-frequency calls, consider benchmarking and using PyCall.without_gvl for long-running operations to mitigate concurrency issues.

Open-Awesome

PyCall

MITCv1.5.2

A Ruby library that enables direct calling of Python functions and modules with automatic type conversion.

GitHub

1.1k stars88 forks0 contributors

What is PyCall?

PyCall is a Ruby gem that enables direct calling of Python functions and modules from Ruby code. It solves the problem of Ruby developers needing to access Python's vast ecosystem of libraries (like NumPy, pandas, or machine learning frameworks) by providing seamless interoperability with automatic type conversion between the two languages.

Target Audience

Ruby developers who need to integrate Python libraries for data science, machine learning, scientific computing, or any task where Python's ecosystem offers superior tools.

Value Proposition

Developers choose PyCall because it provides the most straightforward and Ruby-idiomatic way to call Python code, with automatic type conversion, support for keyword arguments, and intuitive mapping of Python constructs to Ruby syntax, without requiring complex bindings or external processes.

Overview

Calling Python functions from the Ruby language

Use Cases

Best For

Using Python's data science libraries (like pandas or NumPy) within a Ruby on Rails application
Integrating machine learning models written in Python (e.g., TensorFlow, scikit-learn) into Ruby services
Accessing specialized Python-only libraries from Ruby without rewriting functionality
Building hybrid applications that leverage both Ruby's web ecosystem and Python's scientific computing strengths
Prototyping or scripting that requires quick access to Python modules from a Ruby environment
Educational purposes to compare or bridge concepts between Ruby and Python

Not Ideal For

Applications requiring robust multi-threading with concurrent Ruby and Python executions
Environments where Python shared libraries are not available or difficult to install
Projects that need to minimize overhead in cross-language calls

Pros & Cons

Pros

Direct Python Import

Allows importing any Python module as a Ruby module, making functions callable with minimal syntax, as shown in the README example with math.sin.

Automatic Type Conversion

Handles conversions for basic types like numbers, strings, arrays, and hashes without manual intervention, simplifying cross-language data passing.

Intuitive Syntax Mapping

Maps Python constructors to .new and callables to .(), with keyword arguments using Ruby hash syntax, making Python code feel natural in Ruby.

GVL Control for Performance

Provides PyCall.without_gvl to release Ruby's GVL during long Python calls, improving concurrency in blocking operations, as documented in the usage section.

Cons

No Multi-threading Support

Officially does not support multi-threaded use, as admitted in the README, limiting scalability in concurrent applications.

Complex pyenv Setup

Requires rebuilding Python with --enable-shared for pyenv users, an extra non-default step that complicates installation.

Limited Attribute Access

Callable attributes cannot be accessed directly; requires using PyCall.getattr as a workaround, adding syntactic friction.

Frequently Asked Questions

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