.. _faq:

Frequently Asked Questions (FAQ)
================================

A collection of frequently asked questions with answers. If you have a question
and have found an answer, send a PR to add it here!

How should I specify another version of Python?
-----------------------------------------------

One can specify a Python version in the ``environment.yml`` file of a repository
or ``runtime.txt`` file if using ``requirements.txt`` instead of ``environment.yml``.

What versions of Python (or R or Julia...) are supported?
---------------------------------------------------------

Python
~~~~~~

Repo2docker officially supports the following versions of Python
(specified in your :ref:`environment.yml <environment.yml>` or
:ref:`runtime.txt <runtime.txt>` file):

- 3.7 (added in 0.7, default in 0.8)
- 3.6 (default in 0.7 and earlier)
- 3.5
- 2.7

Additional versions may work, as long as the
`base environment <https://github.com/jupyter/repo2docker/blob/master/repo2docker/buildpacks/conda/environment.yml>`_
can be installed for your version of Python.
The most likely source of incompatibility is if one of the packages
in the base environment is not packaged for your Python,
either because the version of the package is too new and your chosen Python is too old,
or vice versa.

I Python 2.7 is specified, a separate environment for the kernel will be
installed with Python 2. The notebook server will run in the default Python 3.6
environment.

Julia
~~~~~

The following versions of Julia are supported (specified in the
:ref:`REQUIRE <REQUIRE>` configuration file):

- 1.0 (added in 0.7)
- 0.7 (added in 0.7)
- 0.6 (default)

R
~

Only R 3.4.4 is currently supported, which is installed via ``apt`` from the
`ubuntu bionic repository <https://packages.ubuntu.com/bionic/r-base>`_.

Can I add executable files to the user's PATH?
----------------------------------------------

Yes! With a :ref:`postBuild` file, you can place any files that should be called
from the command line in the folder ``~/.local/``. This folder will be
available in a user's PATH, and can be run from the command line (or as
a subsequent build step.)

How do I set environment variables?
-----------------------------------

To configure environment variables for all users of a repository use the
:ref:`start <start>` configuration file.

When running repo2docker locally you can use the ``-e`` or ``--env`` command-line
flag for each variable that you want to define.

For example ``jupyter-repo2docker -e VAR1=val1 -e VAR2=val2 ...``

Can I use repo2docker to bootstrap my own Dockerfile?
-----------------------------------------------------

No, you can't.

If you pass the ``--debug`` flag to ``repo2docker``, it outputs the
intermediate Dockerfile that is used to build the docker image. While
it is tempting to copy this as a base for your own Dockerfile, that is
not supported & in most cases will not work. The ``--debug`` output is
just our intermediate generated Dockerfile, and is meant to be built
in a very specific way.  Hence the output of ``--debug`` can not be
built with a normal ``docker build -t .`` or similar traditional
docker command.

Check out the `binder-examples <http://github.com/binder-examples/>`_ GitHub
organization for example repositories you can copy & modify for your own use!

Can I use repo2docker to edit a local host repository within a Docker environment?
----------------------------------------------------------------------------------

Yes: use the ``--editable`` or ``-E`` flag (don't confuse this with
the ``-e`` flag for environment variables), and run repo2docker on a
local repository::

  repo2docker -E my-repository/.

This builds a Docker container from the files in that repository
(using, for example, a ``requirements.txt`` or ``install.R`` file),
then runs that container, while connecting the working directory
inside the container to the local repository outside the
container. For example, in case there is a notebook file (``.ipynb``),
this will open in a local webbrowser, and one can edit it and save
it. The resulting notebook is updated in both the Docker container and
the local repository. Once the container is exited, the changed file
will still be in the local repository.

This allows for easy testing of the container while debugging some
items, as well as using a fully customizable container to edit
notebooks (among others).

.. note::

    Editable mode is a convenience option that will bind the
    repository to the container working directory (usually
    ``$HOME``). If you need to mount to a different location in
    the container, use the ``--volumes`` option instead. Similarly,
    for a fully customized user Dockerfile, this option is not
    guaranteed to work.