oldest-supported-numpy

.. image:: https://img.shields.io/pypi/v/oldest-supported-numpy :target: https://pypi.org/project/oldest-supported-numpy/ :alt: PyPI

About

This is a meta-package which can be used in pyproject.toml files to automatically provide as a build-time dependency the oldest version of NumPy that supports the given Python version and platform. In case of platforms for which NumPy has prebuilt wheels, the provided version also has a prebuilt NumPy wheel.

The reason to use the oldest available NumPy version as a build-time dependency is because of ABI compatibility. Binaries compiled with old NumPy versions are binary compatible with newer NumPy versions, but not vice versa. This meta-package exists to make dealing with this more convenient, without having to duplicate the same list manually in all packages requiring it.

In other words:

.. code:: toml

[build-system]
requires = [
    "wheel",
    "setuptools",
    "numpy==1.13.3; python_version=='3.5'",
    "numpy==1.13.3; python_version=='3.6'",
    "numpy==1.14.5; python_version=='3.7'",
    # more numpy requirements...
]

can be replaced by:

.. code:: toml

[build-system]
requires = ["wheel", "setuptools", "oldest-supported-numpy"]

And as new Python versions are released, the pyproject.toml file does not need to be updated.

Q&A

Why define the NumPy pinnings using install_requires in this repository?

The NumPy version pinnings are defined inside the ``setup.cfg`` file as
``install_requires`` dependencies, rather than as build-time dependencies
inside ``pyproject.toml``. This is deliberate, since NumPy is not actually
required to build wheels of **oldest-supported-numpy**. What we need here
is to make sure that when **oldest-supported-numpy** is installed into
the build environment of a package using it, NumPy gets installed too
as a **runtime** dependency inside the build environment.

Another way to think about this is that since we only publish (universal)
wheels of **oldest-supported-numpy**, the wheel contains no ``pyproject.toml``,
``setup.cfg``, or ``setup.py`` code - it only contains metadata including
dependencies which get installed by pip when **oldest-supported-numpy** is
installed.

Can I use this if my package requires a recent version of NumPy?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In many cases, even though your package may require a version of
NumPy that is more recent than the pinned versions here, this
is often a runtime requirement, i.e. for running (rather than
building) your package. In many cases, unless you use recent
features of the NumPy C API, you will still be able to build your
package with an older version of NumPy and therefore you will still
be able to use **oldest-supported-numpy**. You can still impose a
more recent NumPy requirement in ``install_requires``

What if a bug in NumPy that affects me is fixed only in a newer release?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If **oldest-supported-numpy** pins a ``numpy`` version that is broken for
everyone using a certain OS/platform/interpreter combination, we can update the
``==`` pin to a newer release. In general, building against a newer *bugfix*
release (i.e., a higher ``Y`` value for a ``1.X.Y`` version number) is safe to
do. Newer minor versions will likely not be ABI-compatible, so are much more
difficult to change. If a bug only affects some uses cases (e.g., versions ``<
1.20.3`` don't work on Windows when using ``f2py``), the pin cannot be updated
because it will affect backwards compatibility of **oldest-supported-numpy**.
In that case, it is recommended that you add the needed constraint directly
in your own ``pyproject.toml`` file. For example:

.. code:: toml

    [build-system]
    requires = [
        "wheel",
        "numpy==1.19.0; python_version<='3.8' and platform_system=='Windows' and platform_python_implementation != 'PyPy'",
        "oldest-supported-numpy; python_version>'3.8' or platform_system!='Windows' or platform_python_implementation == 'PyPy'",
        # more requirements (if needed) ...
    ]

Note that when you do this, it is important to ensure the conditions are such
that there is exactly one pin possible for a given platform configuration.
Otherwise your build will fail or ``pip`` may refuse to install your package
*only* on that configuration (so you likely won't see it in CI).
The **oldest-supported-numpy** repository contains tests, so for safety you
may want to implement your constraints in its ``setup.cfg`` and run the
tests with ``pytest`` to validate those constraints.

Why isn't ``oldest-supported-numpy`` available for Conda, Homebrew, Debian, etc.?

The pyproject.toml format is specific to PyPI. Other packaging systems have their own metadata formats and ways of specifying dependencies. Typically they don't need anything like oldest-supported-numpy because either (a) they ship only a single NumPy version for a given release (typically the case for Linux distros and Homebrew), or (b) they have a more explicit way of managing ABI compatibility (see for example conda-forge's pin_compatible feature: https://conda-forge.org/docs/maintainer/knowledge_base.html#linking-numpy).

What about having a catchier name for this package?

The current name is not very catchy as package names go, but it
is very descriptive. This package is only meant to be used in
``pyproject.toml`` files for defining build-time dependencies,
so it's more important to have a descriptive than a catchy name!

What if I think that one of the pinnings is wrong or out of date?

Please feel free to open an issue <https://github.com/scipy/oldest-supported-numpy/issues/new>_ or a pull request if you think something is wrong or could be improved!