[Python-checkins] peps: Update PEP 453 (pip bootstrapping)
nick.coghlan
python-checkins at python.org
Tue Sep 17 16:30:21 CEST 2013
http://hg.python.org/peps/rev/df9e4c301415
changeset: 5126:df9e4c301415
user: Nick Coghlan <ncoghlan at gmail.com>
date: Wed Sep 18 00:30:06 2013 +1000
summary:
Update PEP 453 (pip bootstrapping)
- add MvL as BDFL-Delegate
- clarify that pip is made available by default
- miscellaneous updates to the rationale section
- include a rationale for choosing pip over other tools
- consolidate all the technical details under one heading
- be explicit about the proposed getpip.bootstrap API
- be explicit about the proposed venv API changes
- be explicit about the proposed installer semantics
- be explicit about the documentation impact
- restrict getpip additions to off-by-default security
enhancements (enabled by the installers and pyvenv)
- clarify the Windows PATH is only modified when the relevant
installer option is checked
- request that downstreams that *don't* provide pip at least properly
document that fact
- avoid the term "bundled" (favouring "private copy" or "bootstrapped"
as appropriate)
- name the Python Packaging Authority explicitly in the governance
section and point out that umbrella group now also includes the PyPI
and setuptools maintainers (and more) in addition to the original
group of pip and virtualenv maintainers
- note the hassles CPython has had in the past regarding "externally
maintained" modules
- note why we're not pursuing the idea of bootstrapping into the
user site packages by default
files:
pep-0453.txt | 554 +++++++++++++++++++++++++++-----------
1 files changed, 384 insertions(+), 170 deletions(-)
diff --git a/pep-0453.txt b/pep-0453.txt
--- a/pep-0453.txt
+++ b/pep-0453.txt
@@ -4,22 +4,31 @@
Last-Modified: $Date$
Author: Donald Stufft <donald at stufft.io>,
Nick Coghlan <ncoghlan at gmail.com>
+BDFL-Delegate: Martin von Löwis
Status: Draft
Type: Process
Content-Type: text/x-rst
Created: 10-Aug-2013
-Post-History: 30-Aug-2013, 15-Sep-2013
+Post-History: 30-Aug-2013, 15-Sep-2013, 18-Sep-2013
Abstract
========
-This PEP proposes the inclusion of a method for explicitly bootstrapping
-`pip`_ as the default package manager for Python. It also proposes that the
-distributions of Python available via Python.org will automatically run this
-explicit bootstrapping method and a recommendation to third-party
-redistributors of Python to also provide pip by default (in a way reasonable
-for their distributions).
+This PEP proposes that the `pip`_ package manager be made available by
+default when installing CPython and when creating virtual environments
+using the standard library's ``venv`` module (including via the
+``pyvenv`` command line utility).
+
+To clearly demarcate development responsibilities, and to avoid
+inadvertently downgrading ``pip`` when updating CPython, the proposed
+mechanism to achieve this is to include an explicit `pip`_ bootstrapping
+mechanism in the standard library that is invoked automatically by the
+CPython installers provided on python.org.
+
+The PEP also strongly recommends that CPython redistributors and other Python
+implementations ensure that ``pip`` is available by default, or
+at the very least, explicitly document the fact that it is not included.
Proposal
@@ -39,41 +48,62 @@
Rationale
=========
-Installing a third-party package into a freshly installed Python requires
-first installing the package manager. This requires users ahead of time to
-know what the package manager is, where to get them from, and how to install
-them. The effect of this is that these external projects are required to
-either blindly assume the user already has the package manager installed,
-needs to duplicate the instructions and tell their users how to install
-the package manager, or completely forgo the use of dependencies to ease
-installation concerns for their users.
+Currently, on systems without a platform package manager and repository,
+installing a third-party Python package into a freshly installed Python
+requires first identifying an appropriate package manager and then
+installing it.
-All of the available options have their own drawbacks.
+Even on systems that *do* have a platform package manager, it is unlikely to
+include every package that is available on the Python Package Index, and
+even when a desired third-party package is available, the correct name in
+the platform package manager may not be clear.
-If a project simply assumes a user already has the tooling then they get a
-confusing error message when the installation command doesn't work. Some
-operating may ease this pain by providing a global hook that looks for commands
-that don't exist and suggest an OS package they can install to make the command
-work.
+This means that, to work effectively with the Python Package Index
+ecosystem, users must know which package manager to install, where to get
+it, and how to install it. The effect of this is that third-party Python
+projects are currently required to choose from a variety of undesirable
+alternatives:
-If a project chooses to duplicate the installation instructions and tell their
-users how to install the package manager before telling them how to install
-their own project then whenever these instructions need updates they need
-updating by every project that has duplicated them. This will inevitably not
-happen in every case leaving many different instructions on how to install it
-many of them broken or less than optimal. These additional instructions might
-also confuse users who try to install the package manager a second time
-thinking that it's part of the instructions of installing the project.
+* assume the user already has a suitable cross-platform package manager
+ installed
+* duplicate the instructions and tell their users how to install the
+ package manager
+* completely forgo the use of dependencies to ease installation concerns
+ for their users
-The problem of stale instructions can be alleviated by referencing `pip's
-own bootstrapping instructions
-<http://www.pip-installer.org/en/latest/installing.html>`__, but the user
-experience involved still isn't good (especially on Windows, where
-downloading and running a Python script with the default OS configuration is
+All of these available options have significant drawbacks.
+
+If a project simply assumes a user already has the tooling then beginning
+users may get a confusing error message when the installation command
+doesn't work. Some operating systems may ease this pain by providing a
+global hook that looks for commands that don't exist and suggest an OS
+package they can install to make the command work, but that only works
+on Linux systems with platform package managers. No such assistance is
+availabe for Windows and Mac OS X users. The challenges of dealing with
+this problem are a regular feature of feedback the core Python developers
+receive from professional educators and others introducing new users to
+Python.
+
+If a project chooses to duplicate the installation instructions and tell
+their users how to install the package manager before telling them how to
+install their own project then whenever these instructions need updates
+they need updating by every project that has duplicated them. This is
+particular problematic when there are multiple competing installation
+tools available, and different projects recommend different tools.
+
+This specific problem can be partially alleviated by strongly promoting
+``pip`` as the default installer and recommending that other projects
+reference `pip's own bootstrapping instructions
+<http://www.pip-installer.org/en/latest/installing.html>`__ rather than
+duplicating them. However the user experience created by this approach
+still isn't good (especially on Windows, where downloading and running
+the ``get-pip.py`` bootstrap script with the default OS configuration is
significantly more painful than downloading and running a binary executable
or installer). The situation becomes even more complicated when multiple
-Python versions are involved (for example, parallel installations of Python
-2 and Python 3).
+Python versions are involved (for example, parallel installations of
+Python 2 and Python 3), since that makes it harder to create and maintain
+good platform specific ``pip`` installers independently of the CPython
+installers.
The projects that have decided to forgo dependencies altogether are forced
to either duplicate the efforts of other projects by inventing their own
@@ -84,18 +114,21 @@
duplicated efforts are not automatically updated when upstream releases a new
version.
-By providing the package manager by default it will be easier for users trying
-to install these third party packages as well as easier for the people
-distributing them as they no longer need to pick the lesser evil. This will
-become more important in the future as the Wheel_ package format does not have
-a built in "installer" in the form of ``setup.py`` so users wishing to install
-a Wheel package will need an installer even in the simple case.
+By providing a cross-platform package manager by default it will be easier
+for users trying to install these third-party packages as well as easier
+for the people distributing them as they should now be able to safely assume
+that most users will have the appropriate installation tools available.
+This is expected to become more important in the future as the Wheel_
+package format (deliberately) does not have a built in "installer" in the
+form of ``setup.py`` so users wishing to install from a wheel file will want
+an installer even in the simplest cases.
-Reducing the burden of actually installing a third party package should also
-decrease the pressure to add every useful module to the standard library. This
-will allow additions to the standard library to focus more on why Python should
-have a particular tool out of the box instead of needing to use the difficulty
-in installing a package as justification for inclusion.
+Reducing the burden of actually installing a third-party package should
+also decrease the pressure to add every useful module to the standard
+library. This will allow additions to the standard library to focus more
+on why Python should have a particular tool out of the box instead of
+using the general difficulty of installing third-party packages as
+justification for inclusion.
Providing a standard installation system also helps with bootstrapping
alternate build and installer systems, such as ``setuptools``,
@@ -106,8 +139,29 @@
these utilities.
-Explicit Bootstrapping
-======================
+Why pip?
+--------
+
+``pip`` has been chosen as the preferred default installer, as it
+addresses several design and user experience issues with its predecessor
+``easy_install`` (these issues can't readily be fixed in ``easy_install``
+itself due to backwards compatibility concerns). ``pip`` is also well suited
+to working within the bounds of a single Python runtime installation
+(including associated virtual environments), which is a desirable feature
+for a tool bundled with CPython.
+
+Other tools like ``zc.buildout`` and ``conda`` are more ambitious in their
+aims (and hence substantially better than ``pip`` at handling external
+binary dependencies), so it makes sense for the Python ecosystem to treat
+them more like platform package managers to interoperate with rather than
+as the default cross-platform installation tool. This relationship is
+similar to that between ``pip`` and platform package management systems
+like ``apt`` and ``yum`` (which are also designed to handle arbitrary
+binary dependencies).
+
+
+Explicit bootstrapping mechanism
+================================
An additional module called ``getpip`` will be added to the standard library
whose purpose is to install pip and any of its dependencies into the
@@ -121,9 +175,10 @@
installed so that they can take advantage of the new advances in packaging.
Since any particular version of Python has a much longer staying power than
a version of pip in order to satisfy a user's desire to have the most recent
-version the bootstrap will contact PyPI, find the latest version, download it,
-and then install it. This process is security sensitive, difficult to get
-right, and evolves along with the rest of packaging.
+version the bootstrap will (by default) contact PyPI, find the latest
+version, download it, and then install it. This process is security
+sensitive, difficult to get right, and evolves along with the rest of
+packaging.
Instead of attempting to maintain a "mini pip" for the sole purpose of
installing pip, the ``getpip`` module will, as an implementation detail,
@@ -135,7 +190,7 @@
Not all users will have network access to PyPI whenever they run the
bootstrap. In order to ensure that these users will still be able to
bootstrap pip the bootstrap will fallback to simply installing the included
-copy of pip. The pip ``--no-download`` command-line option will be supported
+copy of pip. The pip ``--no-download`` command line option will be supported
to force installation of the bundled version, without even attempting to
contact PyPI.
@@ -170,84 +225,219 @@
be supported.
+Proposed module API
+-------------------
+
+The proposed ``getpip`` module API is a single ``bootstrap`` function with
+parameter names derived directly from the proposed CLI::
+
+ def bootstrap(download=True, upgrade=False, root=None, user=False,
+ index_url=None, cert=None, proxy=None, timeout=15):
+ """Bootstrap pip into the current Python installation (or the given
+ root directory)"""
+
+The only changes are to replace the ``--no-download`` opt-out option with
+the True-by-default ``download`` option and to replace the hyphen in
+``index-url`` with an underscore to create a legal Python identifier.
+
+
+Invocation from the CPython installers
+--------------------------------------
+
+The CPython Windows and Mac OS X installers will each gain two new options:
+
+* Install pip (the default Python package management utility)?
+* Upgrade pip to the latest version (requires network access)?
+
+Both options will be checked by default, with the option to upgrade pip
+being available for selection only if the option to install pip is checked.
+
+If both options are checked, then the installer will invoke the following
+command with the just installed Python::
+
+ python -m getpip --upgrade
+
+If only the "Install pip" option is checked, then the following command will
+be invoked::
+
+ python -m getpip --upgrade --no-download
+
+This ensures that, by default, installing or updating CPython will ensure
+that either the latest available version of PyPI is installed (directly from
+PyPI if permitted, otherwise whichever is more recent out of an already
+installed version and the private copy inside ``getpip``)
+
+
+Installing from source
+----------------------
+
+While the prebuilt binary installers will be updated to run
+``python -m getpip`` by default, no such change will be made to the
+``make install`` and ``make altinstall`` commands of the source distribution.
+
+``getpip`` itself will still be installed normally (as it is a regular
+part of the standard library), only the implicit installation of pip and
+its dependencies will be skipped.
+
+Keeping the pip bootstrapping as a separate step for ``make``-based
+installations should minimize the changes CPython redistributors need to
+make to their build processes. Avoiding the layer of indirection through
+``make`` for the ``getpip`` invocation also ensures those installing from
+a custom source build can easily force an offline installation of pip,
+install it from a private index server, or skip installing pip entirely.
+
+
+Changes to virtual environments
+-------------------------------
+
+Python 3.3 included a standard library approach to virtual Python environments
+through the ``venv`` module. Since it's release it has become clear that very
+few users have been willing to use this feature directly, in part due to the
+lack of an installer present by default inside of the virtual environment.
+They have instead opted to continue using the ``virtualenv`` package which
+*does* include pip installed by default.
+
+To make the ``venv`` more useful to users it will be modified to issue the
+pip bootstrap by default inside of the new environment while creating it. This
+will allow people the same convenience inside of the virtual environment as
+this PEP provides outside of it as well as bringing the ``venv`` module closer
+to feature parity with the external ``virtualenv`` package, making it a more
+suitable replacement. To handle cases where a user does not wish to have pip
+bootstrapped into their virtual environment a ``--without-pip`` option will be
+added. The ``--no-download`` option will also be supported, to force the
+use of the bundled ``pip`` rather than retrieving the latest version from
+PyPI.
+
+The ``venv.EnvBuilder`` and ``venv.create`` APIs will be updated to accept
+two new parameters: ``with_pip`` (defaulting to ``False``) and
+``bootstrap_options`` (accepting a dictionary of keyword arguments to
+pass to ``getpip.bootstrap`` if ``with_pip`` is set, defaulting to
+``None``).
+
+This particular change will be made only for Python 3.4 and later versions.
+The third-party ``virtualenv`` project will still be needed to obtain a
+consistent cross-version experience in Python 3.3 and 2.7.
+
+
+Documentation
+-------------
+
+The "Installing Python Modules" section of the standard library
+documentation will be updated to recommend the use of the bootstrapped
+`pip` installer. It will give a brief description of the most common
+commands and options, but delegate to the externally maintained ``pip``
+documentation for the full details.
+
+The existing content of the module installation guide will be retained,
+but under a new "Invoking distutils directly" subsection.
+
+
+Bundling CA certificates with CPython
+-------------------------------------
+
+The reference ``getpip`` implementation includes the ``pip`` CA
+bundle along with the rest of pip. This means CPython effectively includes
+a CA bundle that is used solely for ``getpip``.
+
+This is considered desirable, as it ensures that ``pip`` will behave the
+same across all supported versions of Python, even those prior to Python
+3.4 that cannot access the system certificate store on Windows.
+
+
Automatic installation of setuptools
------------------------------------
``pip`` currently depends on ``setuptools`` to handle metadata generation
during the build process, along with some other features. While work is
ongoing to reduce or eliminate this dependency, it is not clear if that
-work will be complete for pip 1.5 (which is the version likely to be
-bundled with Python 3.4.0).
+work will be complete for pip 1.5 (which is the version likely to be current
+when Python 3.4.0 is released).
-This PEP proposes that, if pip still requires it, ``setuptools`` will be
-bundled along with pip itself, and thus installed when running
-``python -m getpip``.
+This PEP proposes that, if pip still requires it as a dependency,
+``getpip`` will include a private copy of ``setuptools`` (in addition
+to the private copy of ``pip``). In normal operation, ``python -m getpip``
+will then download and install the latest version of ``setuptools`` from
+PyPI (as a dependency of ``pip``), while ``python -m getpip --no-download``
+will install the private copy.
-However, this behaviour will be officially declared an implementation
-detail. Other projects which explicitly require setuptools should still
+However, this behaviour is officially considered an implementation
+detail. Other projects which explicitly require ``setuptools`` must still
provide an appropriate dependency declaration, rather than assuming
``setuptools`` will always be installed alongside ``pip``.
+Once pip is able to run ``pip install --upgrade pip`` without needing
+``setuptools`` installed first, then the private copy of ``setuptools``
+will be removed from ``getpip``.
+
Updating the bundled pip
------------------------
In order to keep up with evolutions in packaging as well as providing users
-who are using the offline installation method with as recent version as
-possible, the ``getpip`` module should be updated to the latest versions of
-everything it bootstraps. After each new pip release, and again during the
-preparation for any release of Python, a script, provided as part of this
-PEP, should be run to ensure the bundled packages have been updated to the
-latest versions.
+who are using the offline installation method with as recent version a
+possible the ``getpip`` module will be regularly updated to the latest
+versions of everything it bootstraps.
-This means that maintenance releases of the CPython installers will include
-an updated version of the ``getpip`` bootstrap module.
+After each new pip release, and again during the preparation for any
+release of Python (including feature releases), a script, provided as part
+of this PEP, will be run to ensure the private copies stored in the CPython
+source repository have been updated to the latest versions.
-Feature Addition in Maintenance Releases
+Updating the getpip module API and CLI
+--------------------------------------
+
+Future security updates for pip and PyPI (for example, automatic
+verification of package signatures) may also provide desirable security
+enhancements for the ``getpip`` bootstrapping mechanism.
+
+It is desirable that these features be made available in standard library
+maintenance releases, not just new feature releases.
+
+Accordingly, a slight relaxation of the usual "no new features in
+maintenance releases" rule is proposed for the ``getpip`` module. This
+relaxation also indirectly affects the new ``bootstrap_options`` parameter
+in the ``venv`` module APIs.
+
+Specifically, new security related flags will be permitted, with the
+following restrictions:
+
+- for compatibility with third-party usage of ``getpip`` module (for
+ example, with a private index server), any such flag must be *off* by
+ default in maintenance releases. It *should* be switched on by
+ default in the next feature release.
+- the CPython installers and the ``pyvenv`` CLI in the affected maintenance
+ release should explicitly opt-in to the enhanced security features when
+ automatically bootstrapping ``pip``
+
+This means that maintenance releases of the CPython installers will
+benefit from security enhancements by default, while avoiding breaking
+customised usage of the bootstrap mechanism.
+
+
+Feature addition in maintenance releases
========================================
Adding a new module to the standard library in Python 2.7 and 3.3
maintenance releases breaks the usual policy of "no new features in
maintenance releases".
-It is being proposed in this case as the bootstrapping problem greatly
-affects the experience of new users, especially on Python 2 where many
-Python 3 standard library improvements are available as backports on PyPI,
-but are not included in the Python 2 standard library.
+It is being proposed in this case as the current bootstrapping issues for
+the third-party Python package ecosystem greatly affects the experience of
+new users, especially on Python 2 where many Python 3 standard library
+improvements are available as backports on PyPI, but are not included in
+the Python 2 standard library.
By updating Python 2.7, 3.3 and 3.4 to easily bootstrap the PyPI ecosystem,
-this should aid the vast majority of Python users, rather than only those
-with the freedom to adopt Python 3.4 as soon as it is released.
+this change should aid the vast majority of current Python users, rather
+than only those with the freedom to adopt Python 3.4 as soon as it is
+released.
-This is also a matter of starting as we mean to continue: similar to IDLE
-(see PEP 434), ``getpip`` will be permanently exempted from the "no new
+This is also a matter of starting as we mean to continue: as noted above,
+``getpip`` will have a limited permanent exemption from the "no new
features in maintenance releases" restriction, as it will include (and
-rely on) upgraded versions of ``pip`` even in maintenance releases.
-
-
-Pre-installation
-================
-
-During the installation of Python from Python.org, ``python -m getpip`` should
-be executed, leaving people using the Windows or OSX installers with a working
-copy of pip once the installation has completed. The exact method of this is
-left up to the maintainers of the installers, however if the bootstrapping is
-optional it should be opt-out rather than opt-in.
-
-The Windows and OSX installers distributed by Python.org will automatically
-attempt to run ``python -m getpip`` by default, however the ``make install``
-and ``make altinstall`` commands of the source distribution will not. Note
-that ``getpip`` itself will still be installed normally (as it is a regular
-part of the standard library), only the installation of pip and its
-dependencies will be skipped.
-
-Keeping the pip bootstrapping as a separate step for ``make``-based
-installations should minimize the changes CPython redistributors need to
-make to their build processes. Avoiding the layer of indirection through
-``make`` for the getpip invocation also ensures those installing from a custom
-source build can easily force an offline installation of pip, install it
-from a private index server, or skip installing pip entirely.
+rely on) upgraded private copies of ``pip`` and ``setuptools`` even in
+maintenance releases, and may offer new security related options itself.
Open Question: Uninstallation
@@ -264,60 +454,36 @@
.. note::
- Perhaps the installer needs to be updated to clobber everything in
- site-packages and the Scripts directory, but I would prefer not to make
- this PEP conditional on that change.
+ Perhaps the installer should be updated to clobber everything in
+ site-packages and the Scripts directory when uninstalled (treating them
+ as "data directories" from Python's point of view), but I would prefer
+ not to make this PEP conditional on that change.
Open Question: Script Execution on Windows
==========================================
-While the Windows installer was updated in Python 3.3 to make ``python``
-available on the PATH, no such change was made to include the scripts
-directory. This PEP proposes that this be changed to also add the scripts
-directory.
+While the Windows installer was updated in Python 3.3 to optionally
+make ``python`` available on the PATH, no such change was made to
+include the Scripts directory. This PEP proposes that this installer option
+be changed to also add the Scripts directory to PATH (either always, or
+else as a checked by default suboption).
Without this change, the most reliable way to invoke pip on Windows (without
-tinkering with paths) will actually be ``py -m pip`` (or ``py -3 -m pip``
-if both Python 2 and 3 are installed) rather than simply calling ``pip``.
+tinkering manually with PATH) is actually ``py -m pip`` (or ``py -3 -m pip``
+to select the Python 3 version if both Python 2 and 3 are installed)
+rather than simply calling ``pip``.
Adding the scripts directory to the system PATH would mean that ``pip``
-works reliably in the "only one Python installation" case, with
-``py -m pip`` needed only for the parallel installation case.
+works reliably in the "only one Python installation on the system PATH"
+case, with ``py -m pip`` needed only to select a non-default version in
+the parallel installation case (and outside a virtual environment).
-
-Python Virtual Environments
-===========================
-
-Python 3.3 included a standard library approach to virtual Python environments
-through the ``venv`` module. Since it's release it has become clear that very
-few users have been willing to use this feature in part due to the lack of
-an installer present by default inside of the virtual environment. They have
-instead opted to continue using the ``virtualenv`` package which *does* include
-pip installed by default.
-
-To make the ``venv`` more useful to users it will be modified to issue the
-pip bootstrap by default inside of the new environment while creating it. This
-will allow people the same convenience inside of the virtual environment as
-this PEP provides outside of it as well as bringing the ``venv`` module closer
-to feature parity with the external ``virtualenv`` package, making it a more
-suitable replacement. To handle cases where a user does not wish to have pip
-bootstrapped into their virtual environment a ``--without-pip`` option will be
-added. The ``--no-download`` option will also be supported, to force the
-use of the bundled ``pip`` rather than retrieving the latest version from
-PyPI.
-
-
-Bundling CA Certificates with CPython
-=====================================
-
-The reference ``getpip`` implementation includes the ``pip`` CA
-bundle along with the rest of pip. This means CPython effectively includes
-a CA bundle that is used solely for ``getpip``.
-
-This is considered desirable, as it ensures that ``pip`` will behave the
-same across all supported versions of Python, even those prior to Python
-3.4 that cannot access the system certificate store on Windows.
+While the script invocations on recent versions of Python will run through
+the Python launcher for Windows, this shouldn't cause any issues, as long
+as the Python files in the Scripts directory correctly specify a Python version
+in their shebang line or have an adjacent Windows executable (as
+``easy_install`` and ``pip`` do).
Recommendations for Downstream Distributors
@@ -325,8 +491,8 @@
A common source of Python installations are through downstream distributors
such as the various Linux Distributions [#ubuntu]_ [#debian]_ [#fedora]_, OSX
-package managers [#homebrew]_, or python-specific tools [#conda]_. In order to
-provide a consistent, user-friendly experience to all users of Python
+package managers [#homebrew]_, or Python-specific tools [#conda]_. In order
+to provide a consistent, user-friendly experience to all users of Python
regardless of how they attained Python this PEP recommends and asks that
downstream distributors:
@@ -338,7 +504,8 @@
* Do not remove the bundled copy of pip.
- * This is required for offline installation of pip into a virtual environment.
+ * This is required for offline installation of pip into a virtual
+ environment by the ``venv`` module.
* This is similar to the existing ``virtualenv`` package for which many
downstream distributors have already made exception to the common
"debundling" policy.
@@ -366,29 +533,40 @@
* ``pip install --upgrade pip`` in a virtual environment should not affect
the global installation.
+In the event that a Python redistributor chooses *not* to follow these
+recommendations, we request that they explicitly document this fact and
+provide their users with suitable guidance on translating upstream ``pip``
+based installation instructions into something appropriate for the platform.
+
+Other Python implementations are also encouraged to follow these guidelines
+where applicable.
+
Policies & Governance
=====================
-The maintainers of the bundled software and the CPython core team will work
-together in order to address the needs of both. The bundled software will still
-remain external to CPython and this PEP does not include CPython subsuming the
-responsibilities or decisions of the bundled software. This PEP aims to
-decrease the burden on end users wanting to use third party packages and the
+The maintainers of the bootstrapped software and the CPython core team will
+work together in order to address the needs of both. The bootstrapped
+software will still remain external to CPython and this PEP does not
+include CPython subsuming the development responsibilities or design
+decisions of the bootstrapped software. This PEP aims to decrease the
+burden on end users wanting to use third-party packages and the
decisions inside it are pragmatic ones that represent the trust that the
-Python community has placed in the authors and maintainers of the bundled
-software.
+Python community has already placed in the Python Packaging Authority as
+the authors and maintainers of ``pip``, ``setuptools``, PyPI, ``virtualenv``
+and other related projects.
Backwards Compatibility
-----------------------
-The public API of the ``getpip`` module itself will fall under the typical
-backwards compatibility policy of Python for its standard library. The
-externally developed software that this PEP bundles does not.
+Except for security enhancements (as noted above), the public API of the
+``getpip`` module itself will fall under the typical backwards compatibility
+policy of Python for its standard library. The externally developed software
+that this PEP bundles does not.
-Most importantly, this means that the bundled version of pip may gain new
-features in CPython maintenance releases, and pip continues to operate on
+Most importantly, this means that the bootstrapped version of pip may gain
+new features in CPython maintenance releases, and pip continues to operate on
its own 6 month release cycle rather than CPython's 18-24 month cycle.
@@ -396,29 +574,34 @@
-----------------
Any security update that affects the ``getpip`` module will be shared prior to
-release with the PSRT. The PSRT will then decide if the issue inside warrants
-a security release of Python.
+release with the Python Security Response Team (security at python.org). The
+PSRT will then decide if the reported issue warrants a security release of
+CPython.
Appendix: Rejected Proposals
============================
-Implicit Bootstrap
+Implicit bootstrap
------------------
`PEP439`_, the predecessor for this PEP, proposes its own solution. Its
solution involves shipping a fake ``pip`` command that when executed would
implicitly bootstrap and install pip if it does not already exist. This has
been rejected because it is too "magical". It hides from the end user when
-exactly the pip command will be installed or that it is being installed at all.
-It also does not provide any recommendations or considerations towards
-downstream packagers who wish to manage the globally installed pip through the
-mechanisms typical for their system.
+exactly the pip command will be installed or that it is being installed at
+all. It also does not provide any recommendations or considerations towards
+downstream packagers who wish to manage the globally installed pip through
+the mechanisms typical for their system.
+The implicit bootstrap mechanism also ran into possible permissions issues,
+if a user inadvertently attempted to bootstrap pip without write access to
+the appropriate installation directories.
-Including pip In the Standard Library
--------------------------------------
+
+Including pip directly in the standard library
+----------------------------------------------
Similar to this PEP is the proposal of just including pip in the standard
library. This would ensure that Python always includes pip and fixes all of the
@@ -435,6 +618,37 @@
of the Python community and not just those able to live on the bleeding edge
of Python releases.
+There have also been issues in the past with the "dual maintenance" problem
+if a project continues to be maintained externally while *also* having a
+fork maintained in the standard library. Since external maintenance of
+``pip`` will always be needed to support earlier Python versions, the
+proposed bootstrapping mechanism will becoming the explicit responsibility
+of the CPython core developers (assisted by the pip developers), while
+pip issues reported to the CPython tracker will be migrated to the pip
+issue tracker. There will no doubt still be some user confusion over which
+tracker to use, but hopefully less than has been seen historically when
+including complete public copies of third-party projects in the standard
+library.
+
+Finally, the approach described in this PEP avoids some technical issues
+related to handle CPython maintenance updates when pip has been independently
+updated to a more recent version. The proposed pip-based bootstrapping
+mechanism handles that automatically, since pip and the system installer
+never get into a fight about who owns the pip installation (it is always
+managed through pip, either directly, or indirectly via the getpip bootstrap
+module).
+
+
+Defaulting to --user installation
+---------------------------------
+
+Some consideration was given to bootstrapping pip into the per-user
+site-packages directory by default. However, this behaviour would be
+surprising (as it differs from the default behaviour of pip itself)
+and is also not currently considered reliable (there are some edge cases
+which are not handled correctly when pip is installed into the user
+site-packages directory rather than the system site-packages).
+
.. _Wheel: http://www.python.org/dev/peps/pep-0427/
.. _pip: http://www.pip-installer.org
--
Repository URL: http://hg.python.org/peps
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