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.

Supported Ruby versions

pycall.rb supports Ruby version 2.3 or higher.

Supported Python versions

pycall.rb supports Python version 2.7 or higher.

Note that in Python 2.7 old-style class, that is defined without a super class, is not fully supported in pycall.rb.

Note for pyenv users

pycall.rb requires Python's shared library (e.g. libpython3.7m.so). pyenv does not build the shared library in default, so you need to specify --enable-shared option at the installation like below:

$ env PYTHON_CONFIGURE_OPTS='--enable-shared' pyenv install 3.7.2

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

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

Releasing the RubyVM GVL during Python function calls

You may want to release the RubyVM GVL when you call a Python function that takes very long runtime. PyCall provides PyCall.without_gvl method for such purpose. When PyCall performs python function call, PyCall checks the current context, and then it releases the RubyVM GVL when the current context is in a PyCall.without_gvl's block.

PyCall.without_gvl do
  # In this block, all Python function calls are performed without
  # the GVL acquisition.
  pyobj.long_running_function()
end

# Outside of PyCall.without_gvl block,
# all Python function calls are performed with the GVL acquisition.
pyobj.long_running_function()

Debugging python finder

When you encounter PyCall::PythonNotFound error, you can investigate PyCall's python finder by setting PYCALL_DEBUG_FIND_LIBPYTHON environment variable to 1. You can see the log like below:

$ PYCALL_DEBUG_FIND_LIBPYTHON=1 ruby -rpycall -ePyCall.builtins
DEBUG(find_libpython) find_libpython(nil)
DEBUG(find_libpython) investigate_python_config("python3")
DEBUG(find_libpython) libs: ["Python.framework/Versions/3.7/Python", "Python", "libpython3.7m", "libpython3.7", "libpython"]
DEBUG(find_libpython) libpaths: ["/opt/brew/opt/python/Frameworks/Python.framework/Versions/3.7/lib", "/opt/brew/opt/python/lib", "/opt/brew/opt/python/Frameworks", "/opt/brew/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7", "/opt/brew/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib"]
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/Frameworks/Python.framework/Versions/3.7/lib/Python.framework/Versions/3.7/Python
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/Frameworks/Python.framework/Versions/3.7/lib/Python.framework/Versions/3.7/Python.dylib
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/Frameworks/Python.framework/Versions/3.7/lib/darwin/Python.framework/Versions/3.7/Python
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/Frameworks/Python.framework/Versions/3.7/lib/darwin/Python.framework/Versions/3.7/Python.dylib
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/lib/Python.framework/Versions/3.7/Python
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/lib/Python.framework/Versions/3.7/Python.dylib
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/lib/darwin/Python.framework/Versions/3.7/Python
DEBUG(find_libpython) Unable to find /opt/brew/opt/python/lib/darwin/Python.framework/Versions/3.7/Python.dylib
DEBUG(find_libpython) dlopen("/opt/brew/opt/python/Frameworks/Python.framework/Versions/3.7/Python") = #<Fiddle::Handle:0x00007fc012048650>

PyCall object system

PyCall wraps pointers of Python objects in PyCall::PyPtr objects. PyCall::PyPtr class has two subclasses, PyCall::PyTypePtr and PyCall::PyRubyPtr. PyCall::PyTypePtr is specialized for type (and classobj in 2.7) objects, and PyCall::PyRubyPtr is for the objects that wraps pointers of Ruby objects.

These PyCall::PyPtr objects are used mainly in PyCall infrastructure. Instead, we usually treats the instances of Object, Class, Module, or other classes that are extended by PyCall::PyObjectWrapper module.

PyCall::PyObjectWrapper is a mix-in module for objects that wraps Python objects. A wrapper object should have PyCall::PyPtr object in its instance variable @__pyptr__. PyCall::PyObjectWrapper assumes the existance of @__pyptr__, and provides general translation mechanisms between Ruby object system and Python object system. For example, PyCall::PyObjectWrapper translates Ruby's coerce system into Python's swapped operation protocol.

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.rb.

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.