183 lines
6.1 KiB
ReStructuredText
183 lines
6.1 KiB
ReStructuredText
PEP: 641
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Title: Using an underscore in the version portion of Python 3.10 compatibility tags
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Author: Brett Cannon <brett@python.org>,
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Steve Dower <steve.dower@python.org>,
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Barry Warsaw <barry@python.org>
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PEP-Delegate: Pablo Galindo <pablogsal@python.org>
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Discussions-To: https://discuss.python.org/t/pep-641-using-an-underscore-in-the-version-portion-of-python-3-10-compatibility-tags/5513
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Status: Rejected
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Type: Standards Track
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Content-Type: text/x-rst
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Created: 2020-10-20
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Python-Version: 3.10
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Post-History: 2020-10-21
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Resolution: https://discuss.python.org/t/pep-641-using-an-underscore-in-the-version-portion-of-python-3-10-compatibility-tags/5513/42
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Abstract
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========
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.. note::
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This PEP was rejected due to potential breakage in the community.
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Using the tag system outlined in :pep:`425` (primarily used for wheel
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file names), each release of Python specifies compatibility tags
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(e.g. ``cp39``, ``py39`` for CPython 3.9). For CPython 3.10, this PEP
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proposes using ``3_10`` as the version portion of the tags
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(instead of ``310``).
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Motivation
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==========
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Up to this point, the version portion of compatibility tags used in
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e.g. wheel file names has been a straight concatenation of the major
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and minor versions of Python, both for the CPython interpreter tag and
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the generic, interpreter-agnostic interpreter tag (e.g. ``cp39`` and
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``py39``, respectively). This also applies to the ABI tag
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(e.g. ``cp39``). Thanks to both the major and minor versions being
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single digits, it has been unambiguous what which digit in e.g. ``39``
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represented.
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But starting with Python 3.10, ambiguity comes up as ``310`` does not
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clearly delineate whether the Python version is ``3.10``, ``31.0``, or
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``310`` as the major-only version of Python. Thus using ``3_10`` to
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separate major/minor portions as allowed by :pep:`425` disambiguates
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the Python version being supported.
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Rationale
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=========
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Using ``3_10`` instead of another proposed separator is a restriction
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of :pep:`425`, thus the only options are ``3_10`` or ``310``.
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Specification
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=============
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The ``SOABI`` configure variable and
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``sysconfig.get_config_var('py_version_nodot')`` will be updated to
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use ``3_10`` appropriately.
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Backwards Compatibility
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=======================
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Tools relying on the 'packaging' project [2]_ already expect a
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version specification of ``3_10`` for Python 3.10. Keeping the version
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specifier as ``310`` would require backing that change out and
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updating dependent projects (e.g. pip).
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Switching to ``3_10`` will impact any tools that implicitly rely on
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the convention that the minor version is a single digit. However,
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these are broken regardless of any change here.
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For tools assuming the major version is only the first digit, they
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will require updating if we switch to ``3_10``.
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In non-locale ASCII, ``_`` sorts after any digit, so lexicographic
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sorting matching a sort by Python version of a wheel file name will be
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kept.
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Since PEP 515 (Python 3.6), underscores in numeric literals are ignored.
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This means that ``int("3_10")`` and ``int("310")`` produce the same result,
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and ordering based on conversion to an integer will be preserved.
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**However**, this is still a bad way to sort tags, and the point is raised
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here simply to show that this proposal does not make things worse.
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Security Implications
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=====================
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There are no known security concerns.
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How to Teach This
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=================
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As use of the interpreter tag is mostly machine-based and this PEP
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disambiguates, there should not be any special teaching consideration
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required.
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Reference Implementation
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========================
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A pull request [1]_ already exists adding support to CPython 3.10.
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Support for reading wheel files with this proposed PEP is already
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implemented.
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Rejected Ideas
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==============
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Not making the change
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---------------------
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It was considered to not change the tag and stay with ``310``. The
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argument was it's less work and it won't break any existing
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tooling. But in the end it was thought that the disambiguation is
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better to have.
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Open Issues
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===========
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How far should we take this?
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----------------------------
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Other places where the major and minor version are used could be
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updated to use an underscore as well (e.g. ``.pyc`` files, the import
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path to the zip file for the stdlib). It is not known how useful it
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would be to make this pervasive.
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Standardizing on double digit minor version numbers
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---------------------------------------------------
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An alternative suggestion has been made to disambiguate where the
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major and minor versions start/stop by forcing the minor version to
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always be two digits, padding with a ``0`` as required. The advantages
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of this is it makes the current ``cp310`` interpreter tag accurate,
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thus minimizing breakage. It also does differentiate going forward.
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There are a couple of drawbacks, though. One is the disambiguation
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only exists *if* you know that the minor version number is two digits;
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compare that to ``cp3_10`` which is unambiguous regardless of your
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base knowledge. The potential for a three digit minor version number
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is also not addressed by this two digit requirement.
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There is also the issue of other interpreters not following the
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practice in the past, present, or future. For instance, it is
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unknown if other people have used a three digit version portion of the
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interpreter tag previously for another interpreter where this rule
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would be incorrect. This change would also suggest that interpreters which
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currently have a single digit minor version -- e.g. PyPy 7.3 -- to
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change from ``pp73`` to ``pp703`` or make the switch from their next
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minor release onward (e.g. 7.4 or 8.0). Otherwise this would make this
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rule exclusive to the ``cp`` interpreter type which would make it more
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confusing for people.
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References
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==========
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.. [1] Reference implementation
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(https://github.com/python/cpython/pull/20333)
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.. [2] The 'packaging' project
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(https://pypi.org/project/packaging/)
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Copyright
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=========
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This document is placed in the public domain or under the
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CC0-1.0-Universal license, whichever is more permissive.
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..
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Local Variables:
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mode: indented-text
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indent-tabs-mode: nil
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sentence-end-double-space: t
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fill-column: 70
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coding: utf-8
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End:
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