dmenv: the stupid virtualenv manager

Installation

Download the dmenv installer, then run python installer.py, or python3 installer.py, depending on how your Python interpreter is called. Just make sure it's Python3, not 2.

The script will fetch pre-compiled binaries from GitHub. If you prefer, you can also install rust and install dmenv with cargo install dmenv.

Setup

In order to run, dmenv needs to know the path to the Python3 interpreter you will be using.

To do so, run:

console $ dmenv pythons add default /path/to/python3

Then, dmenv needs a setup.py file. If you don't have one yet, run

dmenv init --name <project name> to generate one. Make sure to read the comments inside and edit it to fit your needs.

Now you are ready to use dmenv!

Here's a description of the main commands:

dmenv lock

Here's what dmenv lock does:

• Create a virtualenv for you with python -m venv in .venv/default. (Make sure to add .venv to your .gitignore).
• Run pip intall --editable .[dev] so that your dev deps are installed, and the scripts listed in entry_points are created.
• Run pip freeze to generate a requirements.lock file.

Now you can add the requirements.lock file to your version control system.

This leads us to the next command.

dmenv install

Now that the complete list of dependencies and their versions is written in the requirements.lock file, anyone can run dmenv install to install all the dependencies and get exactly the same versions you got when you ran dmenv lock.

Hooray reproducible builds!

dmenv run

As a convenience, you can use:dmenv run to run any binary from the virtualenv. If the program you want to run needs command-line options, use a -- to separated them from dmenv options, like so:

console dmenv run -- pytest --collect-only

dmenv upgrade-pip

Tired of pip telling you to upgrade itself? Run dmenv upgrade-pip :)

It's exactly the same as typing dmenv run -- python -m pip install --upgrade pip, but with less keystrokes :P

Using an other python version

To use a different Python version, run dmenv pythons add <version> <path>, when path is the full path to the python binary. For instance: dmenv pythons add 3.8 /path/to/python3.8.

Then you can use Python 3.8 with all the dmenv commands by prefixing them with dmenv --env 3.8.

An other virtualenv will be used in .venv/3.8 so that you can keep your default virtualenv in .venv/default.

Cool, no?

FAQ

Q: How do I upgrade a dependency?
A: Just run dmenv lock again. If something breaks, either fix your code or use more precise version specifiers in setup.py, like foobar < 2.0.

Q: How do I depend on a git specific repo/branch?
A: Edit the requirements.lock by hand like this:

foo==0.1 https://gitlab.com/foo/bar@my-branch

Q: But that sucks and it will disappear when I re-run dmenv lock!
A: See #7. We are looking for a proper solution. In the mean time, feel free to:

• Open a pull request if you've forked an upstream project
• Use a local pipy mirror and a little bit of CI to publish your sources there

Q: Why Rust?
A:

• Because it has excellent support for what we need: manipulate paths and run commands in a cross-platform way
• Because it's my second favorite language
• Because distribution is really easy
• Because by not using Python I'm less likely to depend on pip or virtualenv's internals