PEP: 477 Title: Backport ensurepip (PEP 453) to Python 2.7 Author:
Donald Stufft <donald@stufft.io>, Alyssa 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: 01-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[1],
    modernize[2], or future[3]. 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[4], Wheel[5], and twine[6] 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

Copyright

This document has been placed in the public domain.

[1] six.py

[2] modernize

[3] python-future

[4] setuptools

[5] Wheel

[6] twine