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

First, dmenv needs a Python3 interpreter in PATH, which should be called python or python3. This should already be the case if you've just installed Python3, regardless of your operating system.

Second, dmenv needs a setup.py file to work.

• If you don't have a setup.py yet, you can run dmenv init --name <project name> to generate one. In this case, make sure to read the comments inside and edit it to fit your needs.

• If you already have one, please note that dmenv uses the extras_require keyword with a dev key to specify development dependencies, which you can use to replace your dev-requirements.txt file for instance.

And that's it. Now you are ready to use dmenv!

Here's a description of the main commands:

dmenv lock

Here's what dmenv lock does:

• First, it creates a virtualenv for you with python -m venv in .venv/<version>, where <version> is read from python --version. Make sure to add .venv to your .gitignore! Note that this step is skipped if dmenv detects it is run from an existing virtualenv.

• Then it runs pip intall --editable .[dev] so that your dev deps are installed, and the scripts listed in entry_points are created.

• Finally, it runs 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:

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 interpreter

To use an other Python interpreter than the one in PATH, you can either:

• Modify your PATH environment variable so that it appears there. (For instance, with pyenv).
• Prefix all the dmenv commands with a --python /path/to/other/python flag.

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 at all dmenv is less likely to break if something on your system changes.