Distribution and Library Layout

Anything the package cannot import or run its core path without belongs in base dependencies. Optional integrations, alternative backends and heavyweight accelerators belong in extras, guarded by an import that fails with the exact install command. Development tooling belongs in neither: it belongs in a dependency group.

Because a request for an extra that resolves to nothing is not an error. An unknown or misspelled extra only produces a warning, environment markers on the extra's requirements can all evaluate false, and --no-deps or a stale cached wheel drops them entirely, while the command still exits zero.

It copies the external shared libraries the compiled extension links against into the wheel, rewrites the extension's library search paths so it loads the bundled copies, and mangles their names so they cannot collide with another package's copy of the same library.

Use as_file when something outside Python needs a real filesystem path -- a subprocess argument, or a library that opens the file itself. It is a context manager: an archived resource is extracted per entry, so per-request use copies per request.

It promises a Linux x86-64 binary that runs on any host whose glibc is 2.28 or newer, linking only against a small allowlist of system libraries. Older glibc, or musl instead of glibc, does not match and gets a source build.

Keep it working, make it warn. Emit a DeprecationWarning from the function with stacklevel=2 so the caller's line is blamed, document the replacement and the removal release, ship that for at least one release, then delete it in a major version.

No. PyPI accepts a given filename once and never again, and deleting it does not free the version number. Ship the fix as 1.4.3, then yank 1.4.2 so resolvers skip it while exact pins still install it.

Because the build runs in a fresh, isolated environment containing only the [build-system] requires list. Your activated environment is not on the build's import path, so anything the backend needs must be declared, not merely installed nearby.

Because the tests never imported the wheel. With the repository root first on sys.path, a flat-layout test run imports the working copy, which contains every file; the built distribution can be missing a module and nothing in the run would notice.

Ship stubs when annotations cannot live in the code: a library you do not own, a compiled extension with no Python source, or a codebase that cannot carry them. If you own the source, inline annotations plus the marker win, because stubs drift.

Because no published wheel matched the environment's tags any more, so pip fell back to the source tarball. A new interpreter, a new base image or architecture, or a release that shipped no wheel for that platform all cause it.

Make the surface small and explicit — underscore internals, list the promised names in __all__ at one import path — then treat every listed name as a versioned obligation. Where callers reached into internals, ask what the public API failed to offer before policing them.

python -m zipapp zips a source directory containing a main.py into one .pyz file. CPython imports out of a zip placed on sys.path, so running the archive executes that main.py. The host still needs its own Python.

For a desktop application launched from a shortcut rather than a terminal. On Windows the generated launcher is bound to the windowed interpreter, so no console window appears; on Linux and macOS the two tables produce the same wrapper.

Extras are published metadata on a distribution, so a dev extra ships to every consumer and only works if the project is a package at all. PEP 735 dependency groups live in a top-level [dependency-groups] table, stay in the source tree, and never reach the built wheel.

Run one CI job per operating system and architecture, and inside each job loop the interpreter versions with a wheel-building tool that builds, repairs and smoke-tests each wheel. Use native runners where they exist, cross-compilation or emulation where they do not.

The trailing t marks the free-threaded CPython 3.14 build, which has its own binary interface. A compiled wheel tagged cp314 was built against the standard build's ABI, so it does not match and will not be installed by a free-threaded interpreter.