PyCall: Calling Python functions from the Ruby language

This library provides the features to directly call and partially interoperate with Python from the Ruby language. You can import arbitrary Python modules into Ruby modules, call Python functions with automatic type conversion from Ruby to Python.

Installation

Add this line to your application's Gemfile:

gem 'pycall'

And then execute:

$ bundle

Or install it yourself as:

$ gem install --pre pycall

Usage

Here is a simple example to call Python's math.sin function and compare it to the Math.sin in Ruby:

require 'pycall/import'
include PyCall::Import
pyimport :math
math.sin.(math.pi / 4) - Math.sin(Math::PI / 4)   # => 0.0
#       ^ This period is necessary

Type conversions from Ruby to Python are automatically performed for numeric, boolean, string, arrays, and hashes.

Python function call

In this version of pycall, the all of functions and methods in Python is wrapped as callable objects in Ruby. It means we need to put a priod between the name of function and ( like math.sin.(...) in the above example.

This unnatural notation is a temporary specification, so we should be able to write math.sin(...) in the future.

Wrapping Python classes

NOTE: Currently I'm trying to rewrite class wrapping system, so the content of this section will be changed.

Using PyCall::PyObjectWrapper module, we can create incarnation classes for Python classes in Ruby language. For example, the following script defines a incarnation class for numpy.ndarray class.

require 'pycall'

class Ndarray
  import PyCall::PyObjectWrapper
  wrap_class PyCall.import_module('numpy').ndarray
end

Defineing incarnation classes using wrap_class registeres automatic type conversion, so it changes the class of wrapper object. For example:

require 'pycall/import'
include PyCall::Import
pyimport :numpy, as: :np
x1 = np.array(PyCall.tuple(10))
x1.class   # => PyCall::PyObject

class Ndarray
  import PyCall::PyObjectWrapper
  wrap_class PyCall.import_module('numpy').ndarray
  # NOTE: From here, numpy.ndarray objects are converted to Ndarray objects
end

x2 = np.array(PyCall.tuple(10))
x2.class   # => Ndarray

NOTE: I will write an efficient wrapper for numpy by RubyKaigi 2017.

Specifying the Python version

If you want to use a specific version of Python instead of the default, you can change the Python version by setting the PYTHON environment variable to the path of the python executable.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/mrkn/pycall.

Acknowledgement

PyCall.jl is referred too many times to implement this library.

License

The gem is available as open source under the terms of the MIT License.