Minimal package layout

To start off, we will take a look at the minimal set of files you will need to create an installable Python package. Once you have set these up, your package directory should look like:

├── my_package
│   └──
├── pyproject.toml
└── README.rst

where my_package is the name of your package. We will now take a look at all of these files in turn.


Assuming that you are planning to make your package open source, the most important file you will need to add to your package is an open source license. Many packages in the scientific Python ecosystem use the 3-clause BSD license and we recommend following this or using the MIT license unless you have a good reason not to.

To include the license in your package, create a file called LICENSE and paste the license text into it, making sure that you update the copyright year, authors, and any other required fields


Another important file to include is a README file, which briefly tells users what the package is, and either gives some information about how to install/use it or links to more extensive documentation. We recommend using the reStructuredText (rst) format for your README as this will ensure that the README gets rendered well online, e.g. on GitHub or GitLab and on PyPI.


Python code for your package should live in a sub-directory that has the name of the Python module you want your users to import. This module name should be a valid Python variable name, so cannot start with numbers and cannot include hyphens. Valid package names are example or my_package. For the rest of this guide, we will assume the name of the module is my_package.

Once you have created this directory, the first file to create in it should be a file called which will be the first code to be run when a user imports your package. For now, the only information we will add to this file is the version of the package, since users typically expect to be able to access my_package.__version__ to find out the current package version. While you could simply set e.g.

__version__ = '1.2'

in the file, you then would need to make sure that the version number is in sync with the version number defined in the pyproject.toml file, so a better approach is to put the following in your file

from importlib.metadata import version as _version, PackageNotFoundError
    __version__ = _version(__name__)
except PackageNotFoundError:

This will automatically set __version__ to the global version of the package declared in pyproject.toml or set by the setuptools_scm package (see and pyproject.toml for more details).


The pyproject.toml file is where we will define the metadata about the package. At a minimum, this file should contain the [project] table (defined by PEP621) and the [build-system] table (defined by PEP518).


name = "my-package"
description = "My package description"
readme = "README.rst"
authors = [
    { name = "Your Name", email = "" }
license = { text = "BSD 3-Clause License" }
dependencies = [
dynamic = ["version"]

homepage = "https://link-to-your-project"

The name field is the name your package will have on PyPI. It is not necessarily the same as the module name, so in this case we’ve set the package name to my-package even though the module name is my_package. However, aside from the case where the package name has a hyphen and the module name has an underscore, we strongly recommend making the package and the module name the same to avoid confusion.

Note that the version of the package is not explicitly defined in the file above, (rather, defined as dynamic), because we are using the setuptools_scm package to automatically retrieve the latest version from Git tags. However, if you choose to not use that package, you can explicitly set the version in the [project] section (and remove it from the dynamic list):

version = "0.12"

The description should be a short one-line sentence that will appear next to your package name on PyPI when users search for packages. The readme defines the README.rst file, which will be rendered nicely on the PyPI page for the package.

Finally, the dependencies section is important since it is where you will be declaring the dependencies for your package. The cleanest way to do this is to specify one package per line, as shown above. You can optionally include version restrictions if needed (as shown with astropy>=3.2 above). If your package has no dependencies then you don’t need this option.

A complete list of keywords in [project] can be found in the Python packaging documentation.


In the previous section we discussed the dependencies which can be used to declare run-time dependencies for the package, which are dependencies that are needed for the package to import and run correctly. However, your package may have dependencies that are needed to build the package in the first place. For example, the file will only run correctly if setuptools is installed.

The recommended way to specify build-time dependencies is to define the build-system table:

requires = ["setuptools>=45", "wheel", "setuptools_scm[toml]>=6.2"]
build-backend = 'setuptools.build_meta'

If you choose to not use setuptools_scm, you can remove it from this list.

If you do want to use setuptools_scm you also want to add the following block to enable and configure it:

write_to = "my_package/"

If your package has C extensions that interface with Numpy, you may also need to add Numpy to the above list - see Compiled C/Cython extensions for more details.

A complete list of keywords in [build-system] can be found in PEP518.


zip_safe = false


The zip_safe option should be set to false unless you understand the implications of setting it to true - this option is most relevant when producing application bundles with Python packages.

The packages.find line can be left as-is - this will automatically determine the Python modules to install based on the presence of files.

A complete list of keywords in [tool.setuptools] can be found in the setuptools documentation.


write_to = "my_package/"

The [tool.setuptools_scm] table indicates that we want to use the setuptools_scm package to set the version automatically based on git tags, which will produce version strings such as 0.13 for a stable release, or 0.16.0.dev113+g3d1a8747 for a developer version. The write_to option is not necessary; it will write the parsed version to a with a __version__ variable that can be imported by the package itself.

The file used to be where project metadata was defined, before the advent of setup.cfg and then PEP621 and PEP517 (pyproject.toml). It is no longer necessary to include a file in your project, unless you are building C extensions in your code. However, it can increase compatibility with old versions of pip and other packaging tools.

The minimal file is very simple:

from setuptools import setup


The last file needed for a minimal set-up is the file, which declares which files should be included when you release your package (see Releasing Your Package for more details about how to do this).

This file is simplified by using setuptools_scm, as everything that is git versioned will be included by default. There are likely to be things you want to exclude, such as files generated by the documentation, to do this add:

prune <folder or files>

For example a minimal file for a package using setuptools_scm might look like

prune build
prune docs/_build
prune docs/api
global-exclude *.pyc *.o

which would exclude the autogenerated documentation folders and other build files from the distributions.

If you have chosen not to use setuptools_scm, then this file needs to list files not in the module directory and other non-standard files. So given the files we’ve seen above you would need to include:

include LICENSE
include README.rst
include pyproject.toml

You can find out more about the syntax of this file in Specifying the files to distribute in the Python documentation.

Trying out your package

Once you have committed all of the above files to your repository, you can test out the package by running

pip install .

from the root of the package. Once you have done this, you should be able to start a Python session from a different directory and type e.g.:

>>> import my_package
>>> my_package.__version__