|Title:||Backport ensurepip (PEP 453) to Python 2.7|
|Author:||Donald Stufft <donald at stufft.io> Nick Coghlan <ncoghlan at gmail.com>|
|BDFL-Delegate:||Benjamin Peterson <firstname.lastname@example.org>|
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.
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:
- 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 , modernize , or future . However relying on these tools requires that everyone who uses the project have a tool to install these packages.
- 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.
- 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 , Wheel , and 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.
- 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.
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.
As part of this PEP, the updated packaging distribution and installation guides for Python 3.4 would be backported to Python 2.7.
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.
This document has been placed in the public domain.