python-peps/pep-0477.txt

PEP: 477
Title: Backport ensurepip (PEP 453) to Python 2.7
Version: $Revision$
Last-Modified: $Date$
Author: Donald Stufft <donald@stufft.io>
        Nick Coghlan <ncoghlan@gmail.com>
BDFL-Delegate: Benjamin Peterson <benjamin@python.org>
Status: Final
Type: Standards Track
Content-Type: text/x-rst
Created: 26-Aug-2014
Post-History: 1-Sep-2014
Resolution: https://mail.python.org/pipermail/python-dev/2014-September/136238.html


Abstract
========

This PEP proposes that the ``ensurepip`` module, added to Python 3.4 by PEP
453, be backported to Python 2.7. It also proposes that automatic invocation
of ``ensurepip`` be added to the Python 2.7 Windows and OSX installers. However
it does **not** propose that automatic invocation be added to the ``Makefile``.

It also proposes that the documentation changes for the package distribution
and installation guides be updated to match that in 3.4, which references using
the ``ensurepip`` module to bootstrap the installer.


Rationale
=========

Python 2.7 is effectively a LTS release of Python which represents the end of
the 2.x series and there is still a very large contingent of users whom are
still using Python 2.7 as their primary version. These users, in order to
participate in the wider Python ecosystem, must manually attempt to go out and
find the correct way to bootstrap the packaging tools.

It is the opinion of this PEP that making it as easy as possible for end users
to participate in the wider Python ecosystem is important for 3 primary
reasons:

1. The Python 2.x to 3.x migration has a number of painpoints that are eased by
   a number of third party modules such as six [#six]_, modernize [#modernize]_,
   or future [#future]_. However relying on these tools requires that everyone
   who uses the project have a tool to install these packages.
2. In addition to tooling to aid in migration from Python 2.x to 3.x, there are
   also a number of modules that are *new* in Python 3 for which there are
   backports available on PyPI. This can also aid in the ability for people
   to write 2.x and 3.x compatible software as well as enable them to use some
   of the newer features of Python 3 on Python 2.
3. Users also will need a number of tools in order to create python packages
   that conform to the newer standards that are being proposed. Things like
   setuptools [#setuptools]_, Wheel [#wheel]_, and twine [#twine]_ are enabling
   a safer, faster, and more reliable packaging tool chain. These tools can be
   difficult for people to use if first they must be told how to go out and
   install the package manager.
4. One of Pythons biggest strengths is in the huge ecosystem of libraries and
   projects that have been built on top of it, most of which are distributed
   through PyPI. However, in order to benefit from this wide ecosystem
   meaningfully requires end users, some of which are going to be new, to make
   a decision on which package manager they should get, how to get it, and then
   finally actually installing it first.

Furthermore, alternative implementations of Python are recognizing the benefits
of PEP 453 and both PyPy and Jython have plans to backport ensurepip to their
2.7 runtimes.


Automatic Invocation
====================

PEP 453 has ``ensurepip`` automatically invoked by default in the ``Makefile``
and the Windows and OSX Installers. This allowed it to ensure that, by default,
all users would get Python with pip already installed. This PEP however
believes that while this is fine for the Python 2.7 Windows and Mac OS X
installers it is *not* ok for the Python 2.7 ``Makefile`` in general.

The primary consumers of the ``Makefile`` are downstream package managers which
distribute Python themselves. These downstream distributors typically do not
want pip to be installed via ``ensurepip`` and would prefer that end users
install it with their own package manager. Not invoking ``ensurepip``
automatically from the ``Makefile`` would allow these distributors to simply
ignore the fact that ``ensurepip`` has been backported and still not end up
with pip installed via it.

The primary consumers of the OSX and Windows installers are end users who are
attempting to install Python on their own machine. There is not a package
manager available where these users can install pip into their Python through
a more supported mechanism. For this reason it is the belief of this PEP that
installing by default on OSX and Windows is the best course of action.


Documentation
=============

As part of this PEP, the updated packaging distribution and installation
guides for Python 3.4 would be backported to Python 2.7.


Disabling ensurepip by Downstream Distributors
==============================================

Due to its use in the ``venv`` module, downstream distributors cannot disable
the ``ensurepip`` module in Python 3.4. However, since Python 2.7 has no such
module it is explicitly allowed for downstream distributors to patch the
``ensurepip`` module to prevent it from installing anything.

If a downstream distributor wishes to disable ``ensurepip`` completely in
Python 2.7, they should still at least provide the module and allow
`python -m ensurepip` style invocation. However it should raise errors or
otherwise exit with a non-zero exit code and print out an error on stderr
directing users to what they can/should use instead of ``ensurepip``.


References
==========

.. [#six] `six.py <https://pypi.python.org/pypi/six>`__
.. [#modernize] `modernize <https://pypi.python.org/pypi/modernize>`__
.. [#future] `python-future <https://pypi.python.org/pypi/future>`__
.. [#setuptools] `setuptools <https://pypi.python.org/pypi/setuptools>`__
.. [#wheel] `Wheel <https://pypi.python.org/pypi/wheel>`__
.. [#twine] `twine <https://pypi.python.org/pypi/twine>`__


Copyright
=========

This document has been placed in the public domain.



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