The Python module juliacall

Installation

In the future, the package will be available on PyPI and conda. For now, you can pip install this package directly from github as follows:

pip install git+https://github.com/cjdoris/PythonCall.jl

Developers may wish to clone the repo directly and pip install the module in editable mode. This guarantees you are using the latest version of PythonCall in conjunction with juliacall.

Note also that regardless of installing juliacall, a module called juliacall will always be loaded into the interpreter by PythonCall. This means that other Python packages can always import juliacall.

Getting started

For interactive or scripting use, the simplest way to get started is:

from juliacall import Main as jl

This loads a single variable jl (a ModuleValue) which represents the Main module in Julia, from which all of Julia's functionality is available.

If you are writing a package which uses Julia, then to avoid polluting the global Main namespace you should do:

import juliacall; jl = juliacall.newmodule("SomeName");

Now you can do jl.rand(jl.Bool, 5, 5), which is equivalent to rand(Bool, 5, 5) in Julia.

When a Python value is passed to Julia, then typically it will be converted according to this table with T=Any. Sometimes a more specific type will be used, such as when assigning to an array whose element type is known.

When a Julia value is returned to Python, it will normally be converted according to this table.

Managing Julia dependencies

juliacall manages its Julia dependencies using Pkg for packages and jill for Julia itself. If a suitable version of julia is not found on your system, it will automatically be downloaded and installed into ~/.julia/pythoncall. A Julia environment is automatically created when juliacall is loaded, is activated, and is initialised with at least PythonCall. If you are using a virtual or conda environment then the Julia environment is created there, otherwise a global environment is created at ~/.julia/environments/PythonCall.

If your project requires more Julia dependencies, use the mechanisms below to ensure they are automatically installed.

juliacalldeps.json

If you put a file called juliacalldeps.json in a Python package, then the dependencies therein will be automatically installed into the Julia environment.

Here is an example:

{
    "julia": "1.5",
    "packages": {
        "Example": {
            "uuid": "7876af07-990d-54b4-ab0e-23690620f79a",
            "compat": "0.5",
            "url": "http://github.com/JuliaLang/Example.jl",
            "path": "/path/to/the/package",
            "rev": "master",
            "dev": false, // when true, uses Pkg.dev not Pkg.add
        }
    }
}

All parts are optional, except that the UUID of each package is required.

When juliacall starts, it will ensure the latest compatible version of julia is installed, and will ensure the given packages are installed.

Utilities

newmodule(name)

As(x, T)