[Python VirtualEnv Dockerized]

Tags: #python #virtualenv #docker #venv

Python VirtualEnv Dockerized.md

Python 3 has two ways of handling Virtual Environments:

python3 -m venv /path/to/new/virtual/environment (builtin module)
virtualenv (which venv module is a subset of)

The downside of option 1 is that it only works for the version of the Python 3 interpreter that’s running. For example, if your Python 3 version is 3.6 then you can’t run a virtual environment of packages using Python 3.7

At least with virtualenv you have the option of specifying the Python interpreter you want to use: virtualenv --python=/opt/python-3.3/bin/python.

Source Reference

Once the virtual environment is created you’ll need to activate it: source <path/to/venv>/bin/activate

It’s easy to think of activate as some mysterious magic, a pentacle drawn in blood to keep Python safely trapped. But it’s just software, and fairly simple software at that. The virtualenv documentation will even tell you that activate is “purely a convenience.”

If you go and read the code for activate, it does a number of things:

It figures out what shell you’re running.
It adds a deactivate function to your shell, and messes around with pydoc.
It changes the shell prompt to include the virtualenv name.
It unsets the PYTHONHOME environment variable, if someone happened to set it.
It sets two environment variables: VIRTUAL_ENV and PATH.

The first four are basically irrelevant to Docker usage, so that just leaves the last item. The most important part is setting PATH: PATH is a list of directories which are searched for commands to run. activate simply adds the virtualenv’s bin/ directory to the start of the list.

We can replace activate by setting the appropriate environment variables: Docker’s ENV command applies both subsequent RUNs as well as to the CMD.

The result is the following Dockerfile:

FROM ubuntu:18.04
RUN apt-get update && apt-get install \
  -y --no-install-recommends python3 python3-virtualenv

ENV VIRTUAL_ENV=/opt/venv
RUN python3 -m virtualenv --python=/usr/bin/python3 $VIRTUAL_ENV
ENV PATH="$VIRTUAL_ENV/bin:$PATH"

# Install dependencies:
COPY requirements.txt .
RUN pip install -r requirements.txt

# Run the application:
COPY myapp.py .
CMD ["python", "myapp.py"]