Choose languages for your environment#

You can define many different languages in your configuration files. This page describes how to use some of the more common ones.


Your environment will have Python (and specified dependencies) installed when you use one of the following configuration files:

  • requirements.txt

  • environment.yml


By default, the environment will have Python 3.10.

Changed in version 0.8: Upgraded default Python from 3.6 to 3.7.

Specifying a version of Python#

To specify a specific version of Python, you have two options:

  • Use environment.yml. Conda environments let you define the Python version in environment.yml. To do so, add python=X.X to your dependencies section, like so:

    name: python 2.7
      - python=2.7
      - numpy
  • Use runtime.txt with requirements.txt. If you are using requirements.txt instead of environment.yml, you can specify the Python runtime version in a separate file called runtime.txt. This file contains a single line of the following form:


    For example:


The R Language#

repo2docker supports R, the open source RStudio IDE as well as Jupyter support for R with the IRKernel. To set it up, you need to create a runtime.txt file with the following format:


This will provide you R of given version (such as 4.1, 3.6, etc), and a CRAN snapshot to install libraries from on the given date. You can install more R packages from CRAN by adding a install.R file to your repo. RStudio and IRKernel are installed by default for all R versions. will be used to provide much faster installations via binary packages. For some packages, this might require you install underlying system libraries using apt.txt - Install packages with apt-get - look at the page for the CRAN package you are interested in at to find a list.

repo2docker stopped using the Microsoft mirror MRAN for older R versions after its shutdown in July, 2023.


To build an environment with Julia, include a configuration file called Project.toml. The format of this file is documented at the Julia Pkg.jl documentation. To specify a specific version of Julia to install, put a Julia version in the [compat] section of the Project.toml file, as described here:

Languages not covered here#

If a language is not “officially” supported by a build pack, it can often be installed with a postBuild script. This will run arbitrary bash commands, and can be used to download / install a language.

Using multiple languages at once#

It may also be possible to combine multiple languages in a single environment. The details on how to accomplish this with all possible combinations are outside the scope of this guide. However we recommend that you take a look at the Multi-Language Demo repository for some inspiration.