5.5. Converting versions between PyPI and semver

When packaging for PyPI, your versions are defined through PEP 440. This is the standard version scheme for Python packages and implemented by the packaging.version.Version class.

However, these versions are different from semver versions (cited from PEP 440):

  • The “Major.Minor.Patch” (described in this PEP as “major.minor.micro”) aspects of semantic versioning (clauses 1-8 in the 2.0.0 specification) are fully compatible with the version scheme defined in this PEP, and abiding by these aspects is encouraged.

  • Semantic versions containing a hyphen (pre-releases - clause 10) or a plus sign (builds - clause 11) are not compatible with this PEP and are not permitted in the public version field.

In other words, it’s not always possible to convert between these different versioning schemes without information loss. It depends on what parts are used. The following table gives a mapping between these two versioning schemes:

PyPI Version

Semver version















5.5.1. From PyPI to semver

We distinguish between the following use cases:

  • “Incomplete” versions

    If you only have a major part, this shouldn’t be a problem. The initializer of semver.Version takes care to fill missing parts with zeros (except for major).

    >>> from packaging.version import Version as PyPIVersion
    >>> from semver import Version
    >>> p = PyPIVersion("3.2")
    >>> p.release
    (3, 2)
    >>> Version(*p.release)
    Version(major=3, minor=2, patch=0, prerelease=None, build=None)
  • Major, minor, and patch

    This is the simplest and most compatible approch. Both versioning schemes are compatible without information loss.

    >>> p = PyPIVersion("3.0.0")
    >>> p.base_version
    >>> p.release
    (3, 0, 0)
    >>> Version(*p.release)
    Version(major=3, minor=0, patch=0, prerelease=None, build=None)
  • With pre part only

    A prerelease exists in both versioning schemes. As such, both are a natural candidate. A prelease in PyPI version terms is the same as a “release candidate”, or “rc”.

    >>> p = PyPIVersion("2.1.6.pre5")
    >>> p.base_version
    >>> p.pre
    ('rc', 5)
    >>> pre = "".join([str(i) for i in p.pre])
    >>> Version(*p.release, pre)
    Version(major=2, minor=1, patch=6, prerelease='rc5', build=None)
  • With only development version

    Semver doesn’t have a “development” version. However, we could use Semver’s build part:

    >>> p = PyPIVersion("3.0.0.dev2")
    >>> p.base_version
    >>> p.dev
    >>> Version(*p.release, build=f"dev{p.dev}")
    Version(major=3, minor=0, patch=0, prerelease=None, build='dev2')
  • With a post version

    Semver doesn’t know the concept of a post version. As such, there is currently no way to convert it reliably.

  • Any combination

    There is currently no way to convert a PyPI version which consists of, for example, development and post parts.

You can use the following function to convert a PyPI version into semver:

def convert2semver(ver: packaging.version.Version) -> semver.Version:
    """Converts a PyPI version into a semver version

    :param ver: the PyPI version
    :return: a semver version
    :raises ValueError: if epoch or post parts are used
    if not ver.epoch:
        raise ValueError("Can't convert an epoch to semver")
    if not ver.post:
        raise ValueError("Can't convert a post part to semver")

    pre = None if not ver.pre else "".join([str(i) for i in ver.pre])
    return semver.Version(*ver.release, prerelease=pre, build=ver.dev)

5.5.2. From semver to PyPI

We distinguish between the following use cases:

  • Major, minor, and patch

    >>> from packaging.version import Version as PyPIVersion
    >>> from semver import Version
    >>> v = Version(1, 2, 3)
    >>> PyPIVersion(str(v.finalize_version()))
  • With pre part only

    >>> v = Version(2, 1, 4, prerelease="rc1")
    >>> PyPIVersion(str(v))
  • With only development version

    >>> v = Version(3, 2, 8, build="dev4")
    >>> PyPIVersion(f"{v.finalize_version()}{v.build}")

If you are unsure about the parts of the version, the following function helps to convert the different parts:

def convert2pypi(ver: semver.Version) -> packaging.version.Version:
    """Converts a semver version into a version from PyPI

    A semver prerelease will be converted into a
    prerelease of PyPI.
    A semver build will be converted into a development
    part of PyPI
    :param semver.Version ver: the semver version
    :return: a PyPI version
    v = ver.finalize_version()
    prerelease = ver.prerelease if ver.prerelease else ""
    build = ver.build if ver.build else ""
    return PyPIVersion(f"{v}{prerelease}{build}")