[Distutils] PEP DRAFT - Inclusion of pip bootstrap in Python installation

[Richard Jones]

Hi all,

I present for your deliberation a draft PEP for the inclusion of a pip
bootstrap program in Python 3.4. Discussion of this PEP should remain
here on the distutils SIG.

The PEP is revision controlled in my bitbucket account
https://bitbucket.org/r1chardj0n3s/pypi-pep (this is also where I'm
intending to develop the implementation.)


    Richard

PEP: XXXX
Title: Inclusion of pip bootstrap in Python installation
Version:
Last-Modified:
Author: Richard Jones <richard at python.org>
BDFL-Delegate:  Nick Coghlan <ncoghlan at gmail.com>
Discussions-To: <distutils-sig at python.org>
Status: Draft
Type: Standards Track
Created: 18-Mar-2013
Python-Version: 3.4
Post-History: 19-Mar-2013

Abstract
========

This PEP proposes the inclusion of a pip boostrap executable in the Python
installation to simplify the use of 3rd-party modules by Python users.

This PEP does not propose to include the pip implementation in the Python
standard library. Nor does it propose to implement any package management or
installation mechanisms beyond those provided by PEPs 470 ("The Wheel Binary
Package Format 1.0") and TODO distlib PEP.


Rationale
=========

Currently the user story for installing 3rd-party Python modules is
not as simple as it could be. It requires that all 3rd-party modules inform
the user of how to install the installer, typically via a link to the
installer. That link may be out of date or the steps required to perform the
install of the installer may be enough of a roadblock to prevent the user from
further progress.

Large Python projects which emphasise a low barrier to entry have shied away
from depending on third party packages because of the introduction of this
potential stumbling block for new users.

With the inclusion of the package installer command in the standard Python
installation the barrier to installing additional software is considerably
reduced. It is hoped that this will therefore increase the likelihood that
Python projects will reuse third party software.

It is also hoped that this is reduces the number of proposals to include
more and more software in the Python standard library, and therefore that
more popular Python software is more easily upgradeable beyond requiring
Python installation upgrades.


Proposal
========

Python install includes an executable called "pip" that attempts to import pip
machinery. If it can then the pip command proceeds as normal. If it cannot it
will bootstrap pip by downloading the pip implementation wheel file.
Once installed, the pip command proceeds as normal.

A boostrap is used in the place of a the full pip code so that we don't have
to bundle pip and also the install tool is upgradeable outside of the regular
Python upgrade timeframe and processes.

To avoid issues with sudo we will have the bootstrap default to installing the
pip implementation to the per-user site-packages directory defined in PEP 370
and implemented in Python 2.6/3.0. Since we avoid installing to the system
Python we also avoid conflicting with any other packaging system (on Linux
systems, for example.) If the user is inside a virtual environment (TODO PEP
ref) then the pip implementation will be installed into that virtual
environment.

The bootstrapping process will proceed as follows:

1. The user system has Python (3.4+) installed. In the "scripts" directory of
   the Python installation there is the bootstrap script called "pip".
2. The user will invoke a pip command, typically "pip install <package>", for
   example "pip install Django".
3. The boostrap script will attempt to import the pip implementation. If this
   succeeds, the pip command is processed normally.
4. On failing to import the pip implementation the bootstrap notifies the user
   that it is "upgrading pip" and contacts PyPI to obtain the latest download
   wheel file (see PEP 427.)
5. Upon downloading the file it is installed using the distlib installation
   machinery for wheel packages. Upon completing the installation the user
   is notified that "pip has been upgraded." TODO how is it verified?
6. The pip tool may now import the pip implementation and continues to process
   the requested user command normally.

Users may be running in an environment which cannot access the public Internet
and are relying solely on a local package repository. They would use the "-i"
(Base URL of Python Package Index) argument to the "pip install" command. This
use case will be handled by:

1. Recognising the command-line arguments that specify alternative or additional
   locations to discover packages and attempting to download the package
   from those locations.
2. If the package is not found there then we attempt to donwload it using
   the standard "https://pypi.python.org/pypi/simple/pip" index.
3. If that also fails, for any reason, we indicate to the user the operation
   we were attempting, the reason for failure (if we know it) and display
   further instructions for downloading and installing the file manually.

Manual installation of the pip implementation will be supported through the
manual download of the wheel file and "pip install <downloaded wheel file>".

This installation will not perform standard pip installation steps of saving the
file to a cache directory or updating any local database of installed files.

The download of the pip implementation install file should be performed
securely. The transport from pypi.python.org will be done over HTTPS but the CA
certificate check will most likely not be performed. Therefore we will
utilise the embedded signature support in the wheel format to validate the
downloaded file.

Beyond those arguments controlling index location and download options, the
"pip" boostrap command may support further standard pip options for verbosity,
quietness and logging.

The "--no-install" option to the "pip" command will not affect the bootstrapping
process.

An additional new Python package will be proposed, "pypublish", which will be a
tool for publishing packages to PyPI. It would replace the current "python
setup.py register" and "python setup.py upload" distutils commands. Again
because of the measured Python release cycle and extensive existing Python
installations these commands are difficult to bugfix and extend. Additionally
it is desired that the "register" and "upload" commands be able to be performed
over HTTPS with certificate validation. Since shipping CA certificate keychains
with Python is not really feasible (updating the keychain is quite difficult to
manage) it is desirable that those commands, and the accompanying keychain, be
made installable and upgradeable outside of Python itself.


Implementation
==============

TBD


Risks
=====

The Fedora variant of Linux has had a separate program called "pip" (a Perl
package installer) available for install for some time. The current Python "pip"
program is installed as "pip-python". It is hoped that the Fedora community will
resolve this issue by renaming the Perl installer.

Currently pip depends upon setuptools functionality. It is intended that before
Python 3.4 is shipped that the required functionlity will be present in Python's
standard library as the distlib module, and that pip would be modified to use
that functionality when present. TODO PEP reference for distlib


References
==========

None, so far, beyond the PEPs.


Acknowledgments
===============

Nick Coghlan for his thoughts on the proposal and dealing with the Red Hat
issue.

Jannis Leidel and Carl Meyer for their thoughts.


Copyright
=========

This document has been placed in the public domain.