Flit command line interface

All operations use the flit command, followed by one of a number of subcommands.

Common options

-f <path>, --ini-file <path>

Path to a config file specifying the module to build. The default is pyproject.toml.


Show the version of Flit in use.


Show help on the command-line interface.


Show more detailed logs about what flit is doing.

flit build

Build a wheel and an sdist (tarball) from the package.

--format <format>

Limit to building either wheel or sdist.


Generate a setup.py file in the sdist, so it can be installed by older versions of pip.


Don’t generate a setup.py file in the sdist. This is the default. An sdist built without this will only work with tools that support PEP 517, but the wheel will still be usable by any compatible tool.

Changed in version 3.5: Generating setup.py disabled by default.


Use the files checked in to git or mercurial as the starting list to include in an sdist, and then apply inclusions and exclusions from pyproject.toml.

This is the default for now, but we’re planning to switch to --no-use-vcs as the default in a future version.


Create the sdist starting with only the files inside the installed module or package, along with any inclusions and exclusions defined in pyproject.toml.

With this option, sdists from flit build are equivalent to those built by tools calling Flit as a backend, such as build.

flit publish

Build a wheel and an sdist (tarball) from the package, and upload them to PyPI or another repository.

--format <format>

Limit to publishing either wheel or sdist. You should normally publish the two formats together.


These options affecting what goes in the sdist are described for flit build above.

--repository <repository>

Name of a repository to upload packages to. Should match a section in ~/.pypirc. The default is pypi.

--pypirc <pypirc>

The .pypirc config file to be used. The default is ~/.pypirc.

flit install

Install the package on your system.

By default, the package is installed to the same Python environment that Flit itself is installed in; use --python or FLIT_INSTALL_PYTHON to override this.

If you don’t have permission to modify the environment (e.g. the system Python on Linux), Flit may do a user install instead. Use the --user or --env flags to force this one way or the other, rather than letting Flit guess.

-s, --symlink

Symlink the module into site-packages rather than copying it, so that you can test changes without reinstalling the module.


Create a .pth file in site-packages rather than copying the module, so you can test changes without reinstalling. This is a less elegant alternative to --symlink, but it works on Windows, which typically doesn’t allow symlinks.

--deps <dependency option>

Which dependencies to install. One of all, production, develop, or none. all and develop install the extras test, doc, and dev. Default all.

--extras <extra[,extra,...]>

Which named extra features to install dependencies for. Specify all to install all optional dependencies, or a comma-separated list of extras. Default depends on --deps.


Install the dependencies of this package, but not the package itself.

This can be useful for e.g. building a container image, where your own code is copied or mounted into the container at a later stage.

New in version 3.8.


Do a user-local installation. This is the default if flit is not in a virtualenv or conda env (if the environment’s library directory is read-only and site.ENABLE_USER_SITE is true).


Install into the environment - the opposite of --user. This is the default in a virtualenv or conda env (if the environment’s library directory is writable or site.ENABLE_USER_SITE is false).

--python <path to python>

Install for another Python, identified by the path of the python executable. Using this option, you can install a module for Python 2, for instance. See FLIT_INSTALL_PYTHON if this option is not given.

Changed in version 2.1: Added FLIT_INSTALL_PYTHON and use its value over the Python running Flit when an explicit --python option is not given.


Flit calls pip to do the installation. You can set any of pip’s options using its environment variables.

When you use the --symlink or --pth-file options, pip is used to install dependencies. Otherwise, Flit builds a wheel and then calls pip to install that.

flit init

Create a new pyproject.toml config file by prompting for information about the module in the current directory.

Environment variables


New in version 0.10.

Setting this to any non-empty value will stop flit from making network connections (unless you explicitly ask to upload a package). This is intended for downstream packagers, so if you use this, it’s up to you to ensure any necessary dependencies are installed.


By default, flit install will fail when run as root on POSIX systems, because installing Python modules systemwide is not recommended. Setting this to any non-empty value allows installation as root. It has no effect on Windows.


New in version 0.11.

Set a username, password, and index URL for uploading packages. See uploading packages with environment variables for more information.

Token-based upload to PyPI is supported. To upload using a PyPI token, set FLIT_USERNAME to __token__, and FLIT_PASSWORD to the token value.


New in version 0.13.

Setting this to any non-empty value tells Flit to continue if it detects invalid metadata, instead of failing with an error. Problems will still be reported in the logs, but won’t cause Flit to stop.

If the metadata is invalid, uploading the package to PyPI may fail. This environment variable provides an escape hatch in case Flit incorrectly rejects your valid metadata. If you need to use it and you believe your metadata is valid, please open an issue.


New in version 2.1.

Set a default Python interpreter for flit install to use when --python is not specified. The value can be either an absolute path, or a command name (which will be found in PATH). If this is unset or empty, the module is installed for the copy of Python that is running Flit.


To make reproducible builds, set this to a timestamp as a number of seconds since the start of the year 1970 in UTC, and document the value you used. On Unix systems, you can get a value for the current time by running:

date +%s