Rye is capable (and prefers) to download its own Python distribution over what you might already have on your computer. For CPython, the indygreg/python-build-standalone builds from the PyOxidizer project are used.
The motivation for this is that it makes it easy to switch between Python versions, to have a common experience across different Rye users and to avoid odd bugs caused by changes in behavior.
Unfortunately Python itself does not release binaries (or the right types of binaries) for all operating systems which is why Rye leverages the portable Python builds from PyOxidizer.
Unlike many other Python versions you can install on your computer are non-portable which means that if you move them to a new location on your machine, or you copy it onto another computer (even with the same operating system) they will no longer run. This is undesirable for what Rye wants to do. For one we want the same experience for any of the Python developers, no matter which operating system they used. Secondly we want to enable self-contained Python builds later, which requires that the Python installation is portable.
To achieve this, the Python builds we use come with some changes that are different from a regular Python build.
The following changes to a regular Python versions you should be aware of:
readlineis GPL2 licensed and this is a hazard for redistributions. As such, the portable Python builds link against the more freely licensed
dbm.gnuis unavailable. This is a rather uncommonly used module and the standard library provides alternatives.
Additionally due to how these builds are created, there are some other quirks you might run into related to terminal support or TKinter. Some of these issues are collected in the FAQ. Additionally the Python Standalone Builds have a Behavior Quirks page.
Portable CPython builds are downloaded from GitHub (indygreg/python-build-standalone/releases) and SHA256 hashes are generally validated. Some older versions might not have hashes available in which case the validation is skipped.
When you pin a Python version to
email@example.com (or just
major.minor.patch) then Rye will automatically download the right version
for you whenever it is needed. If a custom toolchain has already been registered with that name and
version, that this is used instead.