# PEP440 in rust

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A library for python version numbers and specifiers, implementing
[PEP 440](https://peps.python.org/pep-0440).
See [Reimplementing PEP 440](https://cohost.org/konstin/post/514863-reimplementing-pep-4) for some background.

Higher level bindings to the requirements syntax are available in [pep508_rs](https://github.com/konstin/pep508_rs).

```rust
use std::str::FromStr;
use pep440_rs::{parse_version_specifiers, Version, VersionSpecifier};

let version = Version::from_str("1.19").unwrap();
let version_specifier = VersionSpecifier::from_str("==1.*").unwrap();
assert!(version_specifier.contains(&version));
let version_specifiers = parse_version_specifiers(">=1.16, <2.0").unwrap();
assert!(version_specifiers.contains(&version));
```

In python (`pip install pep440_rs`):

```python
from pep440_rs import Version, VersionSpecifier

assert Version("1.1a1").any_prerelease()
assert Version("1.1.dev2").any_prerelease()
assert not Version("1.1").any_prerelease()
assert VersionSpecifier(">=1.0").contains(Version("1.1a1"))
assert not VersionSpecifier(">=1.1").contains(Version("1.1a1"))
# Note that python comparisons are the version ordering, not the version specifiers operators
assert Version("1.1") >= Version("1.1a1")
assert Version("2.0") in VersionSpecifier("==2")
```

PEP 440 has a lot of unintuitive features, including:

* An epoch that you can prefix the version which, e.g. `1!1.2.3`. Lower epoch always means lower version (`1.0 <=2!0.1`)
* post versions, which can be attached to both stable releases and prereleases
* dev versions, which can be attached to sbpth table releases and prereleases. When attached to a prerelease the dev
  version is ordered just below the normal prerelease, however when attached to a stable version, the dev version is
  sorted before a prereleases
* prerelease handling is a mess: "Pre-releases of any kind, including developmental releases, are implicitly excluded
  from all version specifiers, unless they are already present on the system, explicitly requested by the user, or if
  the only available version that satisfies the version specifier is a pre-release.". This means that we can't say
  whether a specifier matches without also looking at the environment
* prelease vs. prerelease incl. dev is fuzzy
* local versions on top of all the others, which are added with a + and have implicitly typed string and number segments
* no semver-caret (`^`), but a pseudo-semver tilde (`~=`)
* ordering contradicts matching: We have e.g. `1.0+local > 1.0` when sorting, but `==1.0` matches `1.0+local`. While the
  ordering of versions itself is a total order the version matching needs to catch all sorts of special cases
