Regex to match PEP440 compliant version strings

PEP 440 lays out what is the accepted format for version strings of Python packages.

These can be simple, like: 0.0.1

Or complicated, like: 2016!1.0-alpha1.dev2

What is a suitable regex which could be used for finding and validating such strings?

I had the same question. This is the most thorough regex pattern I could find. PEP440 links to the codebase of the packaging library in it's references section.

pip install packaging

To access just the pattern string you can use the global

from packaging import version
version.VERSION_PATTERN

See: https://github.com/pypa/packaging/blob/21.3/packaging/version.py#L225-L254

VERSION_PATTERN = r"""
    v?
    (?:
        (?:(?P<epoch>[0-9]+)!)?                           # epoch
        (?P<release>[0-9]+(?:\.[0-9]+)*)                  # release segment
        (?P<pre>                                          # pre-release
            [-_\.]?
            (?P<pre_l>(a|b|c|rc|alpha|beta|pre|preview))
            [-_\.]?
            (?P<pre_n>[0-9]+)?
        )?
        (?P<post>                                         # post release
            (?:-(?P<post_n1>[0-9]+))
            |
            (?:
                [-_\.]?
                (?P<post_l>post|rev|r)
                [-_\.]?
                (?P<post_n2>[0-9]+)?
            )
        )?
        (?P<dev>                                          # dev release
            [-_\.]?
            (?P<dev_l>dev)
            [-_\.]?
            (?P<dev_n>[0-9]+)?
        )?
    )
    (?:\+(?P<local>[a-z0-9]+(?:[-_\.][a-z0-9]+)*))?       # local version
"""

Of course this example is specific to Python's flavor of regex.