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Manage venvs and dependencies for flit projects.


  • Supports the most modern metadata format described in PEP 621.
  • Locks dependencies using pip-tools.
  • Multiple venvs per project to ensure a better isolation of environments.
  • No vendor lock, under-the-hood uses popular and well-maintained technologies and tool-agnostic formats.
  • Cross-platform.
  • Battle-tested.


python3 -m pip install flitenv



  1. The project stores metadata in a flit-compatible format, as described in the flit documentation. The recommended ways is to us the new [project] section introduced in PEP 621.
  2. Direct required production dependencies of the project are described in dependencies list. This environment is called main.
  3. Development environments are described in the [project.optional-dependencies] section. Good examples of such environments are test, lint, and doc.
  4. For each environment, flitenv will create a separate venv in .venvs to ensure a good isolation.
  5. "Lock file" is a file with exact versions of all dependencies of the project in the given environment, including the transitive ones.
  6. Flitenv uses requirements.txt files generated by pip-tools as lock files.
  7. It is recommend to generate a lock file for (and only for) the main environment.
  8. flitenv follows the flit philosophy. It provides only the most helpful and flexible commands, and you can do anything you ever need by combining them with each other and with other tools.

Below are usage examples. Each example uses lint as the target environment and flake8 as a command we want to run in this environment.

  • flitenv install lint: install dependencies. If the venv doesn't exist, it will be created. Can also be used to upgrade dependencies when the lock file has been changed.
  • flitenv run lint flake8: run a command. If the venv doesn't exist, it will be created, and the dependencies will be installed.
  • flitenv lock lint: generate lock file (requirements-lint.txt) for the env.
  • flitenv lock main: generate lock file (requirements.txt) for the main env. If there is no env-specific lock file, this one will be used instead.
  • flitenv lock main -c ../other-project/requirements.txt: generate lock file using lock file from another project as a reference. It allows to ensure compatibility of lock files accross multiple projects.
  • rm requirements.txt && flitenv lock main: upgrade all dependencies in the lock file.
  • rm -rf .venvs/lint && flitenv install lint: re-create the venv. It is useful to ensure that all old dependencies are removed.
  • flit build: build a distribution for the project.
  • flit install --symlink --python $(which python3.9) --deps=none: symlink the project into the given Python interpreter without installing dependencies. It is helpful if you want to have nice go-to-definition in vscode across multiple projects.