304 lines
12 KiB
Plaintext
304 lines
12 KiB
Plaintext
PEP: 427
|
||
Title: The Wheel Binary Package Format 1.0
|
||
Version: $Revision$
|
||
Last-Modified: $Date$
|
||
Author: Daniel Holth <dholth@fastmail.fm>
|
||
Discussions-To: Distutils SIG
|
||
Status: Draft
|
||
Type: Standards Track
|
||
Content-Type: text/x-rst
|
||
Created: 20 Sep 2012
|
||
|
||
|
||
Abstract
|
||
========
|
||
|
||
This PEP describes a built-package format for Python called wheel.
|
||
|
||
A wheel is a ZIP-format archive with a specially formatted file name and
|
||
the .whl extension. It contains a single distribution nearly as it would
|
||
be installed according to PEP 376 with a particular installation scheme.
|
||
A wheel file may be installed by simply unpacking into site-packages
|
||
with the standard ‘unzip’ tool, while preserving enough information
|
||
to spread its contents out onto their final paths at any later time.
|
||
|
||
Rationale
|
||
=========
|
||
|
||
Python needs a package format that is easier to install than sdist.
|
||
Python’s sdist packages are defined by and require the distutils and
|
||
setuptools build systems, running arbitrary code to build-and-install,
|
||
and re-compile, code just so it can be installed into a new virtualenv.
|
||
This system of conflating build-install is slow, hard to maintain, and
|
||
hinders innovation in both build systems and installers.
|
||
|
||
Wheel attempts to remedy these problems by providing a simpler interface
|
||
between the build system and the installer. The wheel binary package
|
||
format frees installers from having to know about the build system,
|
||
saves time by amortizing compile time over many installations, and
|
||
removes the need to install a build system in the target environment.
|
||
|
||
Details
|
||
=======
|
||
|
||
Installing a wheel ‘distribution-1.0.py32.none.any.whl’
|
||
-------------------------------------------------------
|
||
|
||
#. Unpack.
|
||
|
||
a. Parse distribution-1.0.dist-info/WHEEL.
|
||
b. Check that installer is compatible with Wheel-Version. Warn if minor
|
||
version is greater, abort if major version is greater.
|
||
c. If Root-Is-Purelib == ‘true’, unpack archive into purelib
|
||
(site-packages).
|
||
d. Else unpack archive into platlib (site-packages).
|
||
|
||
#. Spread.
|
||
|
||
a. Unpacked archive includes distribution-1.0.dist-info/ and (if there
|
||
is data) distribution-1.0.data/
|
||
b. Move each subtree of distribution-1.0.data/ onto its destination
|
||
path. Each subdirectory of distribution-1.0.data/ is a key into
|
||
sysconfig.get\_paths(), such as
|
||
distribution-1.0.data/(config\|purelib\|platlib\|scripts).
|
||
See` <http://docs.python.org/dev/packaging/setupcfg.html#resources>`_`http://docs.python.org/dev/packaging/setupcfg.html#resources <http://docs.python.org/dev/packaging/setupcfg.html#resources>`_
|
||
c. If applicable, update scripts starting with “#!python” to point to
|
||
the correct interpreter.
|
||
d. Update distribution-1.0.dist.info/RECORD with the installed paths.
|
||
e. Remove empty distribution-1.0.data directory.
|
||
|
||
File Format
|
||
-----------
|
||
|
||
File name convention
|
||
~~~~~~~~~~~~~~~~~~~~
|
||
|
||
The wheel filename is {distribution}-{version}(-{build tag})?-{python
|
||
tag}-{abi tag}-{platform tag}.whl
|
||
|
||
distribution
|
||
Distribution name, e.g. ‘django’, ‘pyramid’
|
||
|
||
version
|
||
PEP-386 compliant version, e.g. 1.0
|
||
|
||
build tag
|
||
Optional build number. Must start with a digit. A tie breaker if two
|
||
wheels have the same version. Sort as None if unspecified, else sort
|
||
the initial digits as a number, and the remainder lexicographically.
|
||
|
||
language implementation and version tag
|
||
‘py27’ ‘py2’ ‘py3’
|
||
|
||
abi tag
|
||
‘cp33m’, ‘abi3’, ‘none’
|
||
|
||
platform tag
|
||
‘linux\_x86\_64’, ‘any’
|
||
|
||
For example, distribution-1.0-1-py27-none-any.whl is the first build
|
||
of a package called 'distribution', and is compatible with Python 2.7
|
||
(any Python 2.7 implementation), with no abi (pure Python), on any CPU
|
||
architecture.
|
||
|
||
The last three components of the filename before the extension are
|
||
called “compatibility tags.” The compatibility tags express
|
||
the package’s basic interpreter requirements and are detailed
|
||
in `PEP 425 <http://hg.python.org/peps/file/tip/pep-0425.txt>`_.
|
||
|
||
|
||
File contents
|
||
~~~~~~~~~~~~~
|
||
|
||
#. Wheel files contain a folder {distribution}-{version}.dist-info/ with
|
||
the PEP 426 metadata (Metadata version 1.3 or greater) and an
|
||
additional file WHEEL with metadata about the archive itself.
|
||
#. The root of a .whl is installed into one of purelib or platlib.
|
||
#. Wheel files contain metadata about the wheel format itself in
|
||
{distribution}-{version}.dist-info/WHEEL::
|
||
|
||
Wheel-Version: 1.0
|
||
Generator: bdist_wheel 0.7
|
||
Root-Is-Purelib: true
|
||
|
||
#. Wheel-Version is the version number of the Wheel specification.
|
||
Generator is the name and optionally the version of the software that
|
||
produced the archive. Root-Is-Purelib is true if the top level
|
||
directory of the archive should be installed into purelib; otherwise
|
||
the root should be installed into platlib.
|
||
#. A wheel installer should warn if Wheel-Version is greater than the
|
||
version it supports, and fail if Wheel-Version has a greater major
|
||
version than the version it supports.
|
||
#. If a .whl contains scripts, both purelib and platlib, or any other
|
||
files that are not installed on sys.path, they are found in
|
||
{distribution}-{version}.data/{key}, where {key} is an index into
|
||
sysconfig.get\_paths().
|
||
#. Wheel, being an installation format that is intended to work across
|
||
multiple versions of Python, does not generally include .pyc files.
|
||
#. Wheel does not contain setup.py or setup.cfg.
|
||
|
||
|
||
The .dist-info directory
|
||
^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
#. Wheel .dist-info directories include at a minimum METADATA, WHEEL,
|
||
and RECORD.
|
||
#. METADATA is the PEP 426 metadata (Metadata version 1.3 or greater)
|
||
#. WHEEL is the wheel metadata, specific to a build of the package.
|
||
#. RECORD is a list of (almost) all the files in the wheel and their
|
||
secure hashes. Unlike PEP 376, every file except RECORD, which cannot
|
||
contain a hash of itself, must include its hash. The hash algorithm
|
||
must be sha256 or better; specifically, md5 and sha1 are not
|
||
permitted, as signed wheel files rely on the strong hashes in RECORD to
|
||
validate the integrity of the archive.
|
||
#. INSTALLER and REQUESTED are not included in the archive.
|
||
#. RECORD.jws is used for digital signatures. It is not mentioned in
|
||
RECORD.
|
||
#. RECORD.p7s is reserved as a courtesy to anyone who would prefer to
|
||
use s/mime signatures to secure their wheel files. It is not
|
||
mentioned in RECORD.
|
||
#. During extraction, wheel installers verify all the hashes in RECORD
|
||
against the file contents. Apart from RECORD and its signatures,
|
||
installation will fail if any file in the archive is not both
|
||
mentioned and correctly hashed in RECORD.
|
||
|
||
|
||
The .data directory
|
||
^^^^^^^^^^^^^^^^^^^
|
||
|
||
Any file that is not normally installed inside site-packages goes into
|
||
the .data directory, named as the .dist-info directory but with the
|
||
.data/ extension::
|
||
|
||
distribution-1.0.dist-info/
|
||
|
||
distribution-1.0.data/
|
||
|
||
The .data directory contains subdirectories named after the keys of
|
||
sysconfig.get\_paths(), and those subdirectories contain the scripts,
|
||
headers, documentation and so forth from the distribution. During
|
||
installation the contents of these subdirectories are moved onto their
|
||
destination paths.
|
||
|
||
|
||
Signed wheel files
|
||
------------------
|
||
|
||
Wheel files include an extended RECORD that enables digital signatures.
|
||
PEP 376’s RECORD is altered to include
|
||
digestname=urlsafe\_b64encode\_nopad(digest) (urlsafe base64 encoding
|
||
with no trailing = characters) as the second column instead of an
|
||
md5sum. All possible entries are hashed, including any generated files
|
||
such as .pyc files, but not RECORD. For example::
|
||
|
||
file.py,sha256=AVTFPZpEKzuHr7OvQZmhaU3LvwKz06AJw8mT\_pNh2yI,3144
|
||
distribution-1.0.dist-info/RECORD,,
|
||
|
||
RECORD.jws is not mentioned in RECORD at all. Every other file in the
|
||
archive must have a correct hash in RECORD, or the installation will
|
||
fail.
|
||
|
||
The signature is one or more JSON Web Signature JSON Serialization
|
||
(JWS-JS) signatures stored in a file RECORD.jws adjacent to RECORD.
|
||
|
||
A signature-aware installer can be instructed to check for a particular
|
||
Ed25519 public key by using an extended “extras” syntax.::
|
||
|
||
# request a normal optional feature "extra", and indicate
|
||
# the package should be signed by a particular
|
||
# urlsafe-b64encode-nopad encoded ed25519 public key:
|
||
package[extra, ed25519=ouBJlTJJ4SJXoy8Bi1KRlewWLU6JW7HUXTgvU1YRuiA]
|
||
|
||
An application could distribute a requires.txt file with many such lines
|
||
for all its dependencies and their public keys. By installing from this
|
||
file an application’s users would know whether the applicaton’s
|
||
dependencies came from the correct publishers.
|
||
|
||
Applications that wish to “fail open” for backwards compatibility with
|
||
non-signature-aware installers should specify that their package
|
||
provides the extra ed25519=(key) with no associated dependencies.
|
||
|
||
Key distribution is outside the scope of this spec. Public wheel signing
|
||
keys could be signed with the packager’s GPG key or stored at
|
||
an https://-protected URL.
|
||
|
||
|
||
JSON Web Signatures Extensions
|
||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
||
The Ed25519 algorithm is used as an extension to the JSON Web Signatures
|
||
specification. Wheel uses alg="Ed25519" in the header. The key attribute
|
||
holds the signature’s public JSON Web Key. For JSON Web Key / JSON
|
||
Private Key the verifying (public) key is called vk and the signing
|
||
(private) key is called sk.
|
||
|
||
Example header::
|
||
|
||
{
|
||
"alg": "Ed25519",
|
||
"typ": "JWT",
|
||
"key": {
|
||
"alg": "Ed25519",
|
||
"vk": "tmAYCrSfj8gtJ10v3VkvW7jOndKmQIYE12hgnFu3cvk"
|
||
}
|
||
}
|
||
|
||
A future version of wheel may omit typ.
|
||
|
||
Example payload::
|
||
|
||
{ "hash": "sha256=ADD-r2urObZHcxBW3Cr-vDCu5RJwT4CaRTHiFmbcIYY" }
|
||
|
||
A future version of wheel may include timestamps in the payload or in
|
||
the signature.
|
||
|
||
See
|
||
|
||
- http://self-issued.info/docs/draft-ietf-jose-json-web-signature.html
|
||
- http://self-issued.info/docs/draft-jones-json-web-signature-json-serialization-01.html
|
||
- http://self-issued.info/docs/draft-ietf-jose-json-web-key-05.html
|
||
- http://self-issued.info/docs/draft-jones-jose-json-private-key-00.html
|
||
|
||
|
||
Comparison to .egg
|
||
------------------
|
||
|
||
#. Wheel is an installation format; egg is importable. Wheel archives do
|
||
not need to include .pyc and are less tied to a specific Python
|
||
version or implementation. Wheel can install (pure Python) packages
|
||
built with previous versions of Python so you don’t always have to
|
||
wait for the packager to catch up.
|
||
#. Wheel uses .dist-info directories; egg uses .egg-info. Wheel is
|
||
compatible with the new world of Python packaging and the new
|
||
concepts it brings.
|
||
#. Wheel has a richer file naming convention for today’s
|
||
multi-implementation world. A single wheel archive can indicate its
|
||
compatibility with a number of Python language versions and
|
||
implementations, ABIs, and system architectures. Historically the ABI
|
||
has been specific to a CPython release, wheel is ready for the stable
|
||
ABI.
|
||
#. Wheel is lossless. The first wheel implementation bdist\_wheel always
|
||
generates egg-info, and then converts it to a .whl. It is also
|
||
possible to convert existing eggs and bdist\_wininst distributions.
|
||
#. Wheel is versioned. Every wheel file contains the version of the
|
||
wheel specification and the implementation that packaged it.
|
||
Hopefully the next migration can simply be to Wheel 2.0.
|
||
#. Wheel is a reference to the other Python.
|
||
|
||
|
||
FAQ
|
||
===
|
||
|
||
Wheel defines a .data directory. Should I put all my data there?
|
||
No. The word 'data' is used only because it is short, and is only
|
||
meant to indicate files that are not installed into site-packages.
|
||
This specification does not have an opinion on how you should organize
|
||
your code.
|
||
|
||
|
||
Copyright
|
||
=========
|
||
|
||
This document has been placed into the public domain.
|
||
|