PEP 453 – Explicit bootstrapping of pip in Python installations
- Donald Stufft <donald at stufft.io>, Nick Coghlan <ncoghlan at gmail.com>
- Martin von Löwis
- Standards Track
- 30-Aug-2013, 15-Sep-2013, 18-Sep-2013, 19-Sep-2013, 23-Sep-2013, 29-Sep-2013, 13-Oct-2013, 20-Oct-2013
- Python-Dev message
Table of Contents
- PEP Acceptance
- Proposal Overview
- Explicit bootstrapping mechanism
- Security considerations
- Reliability considerations
- Implementation strategy
- Integration timeline
- Proposed CLI
- Proposed module API
- Invocation from the CPython installers
- Installing from source
- Changes to virtual environments
- Bundling CA certificates with CPython
- Automatic installation of setuptools
- Updating the private copy of pip
- Updating the ensurepip module API and CLI
- Script Execution on Windows
- Recommendations for Downstream Distributors
- Policies & Governance
- Appendix: Rejected Proposals
This PEP proposes that the
Installing Python Modules guide in
Python 2.7, 3.3 and 3.4 be updated to officially recommend the use of
as the default installer for Python packages, and that appropriate technical
changes be made in Python 3.4 to provide
pip by default in support of
This PEP was accepted for inclusion in Python 3.4 by Martin von Löwis on Tuesday 22nd October, 2013.
Issue 19347 has been created to track the implementation of this PEP.
There are two related, but distinct rationales for the proposal in this PEP. The first relates to the experience of new users, while the second relates to better enabling the evolution of the broader Python packaging ecosystem.
Improving the new user experience
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.
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.
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:
- 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.
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 systems with platform package managers that include a package that provides the relevant cross-platform installer command (such as many major Linux distributions). No such assistance is available for Windows and Mac OS X users, or more conservative Linux distributions. The challenges of dealing with this problem for beginners (who are often also completely new to programming, the use of command line tools and editing system environment variables) 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 rather than
duplicating them. However the user experience created by this approach
still isn’t particularly good (although there is an effort under way to
create a combined Windows installer for
pip and its dependencies that
should improve matters on that platform, and Mac OS X and *nix platforms
wget and hence the ability to easily download and run the
bootstrap scripts from the command line).
The projects that have decided to forgo dependencies altogether are forced to either duplicate the efforts of other projects by inventing their own solutions to problems or are required to simply include the other projects in their own source trees. Both of these options present their own problems either in duplicating maintenance work across the ecosystem or potentially leaving users vulnerable to security issues because the included code or duplicated efforts are not automatically updated when upstream releases a new version.
By officially recommending and providing by default a specific cross-platform
package manager 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 (or access to clear instructions on
how to obtain them). 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, and why it is reasonable for that package to adopt the standard library’s 18-24 month feature release cycle, 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
conda. So long as
pip install <tool> works, then a standard
Python-specific installer provides a reasonably secure, cross platform
mechanism to get access to these utilities.
Enabling the evolution of the broader Python packaging ecosystem
As no new packaging standard can achieve widespread adoption without a transition strategy that covers the versions of Python that are in widespread current use (rather than merely future versions, like most language features), the change proposed in this PEP is considered a necessary step in the evolution of the Python packaging ecosystem
The broader community has embraced the Python Package Index as a mechanism for distributing and installing Python software, but the different concerns of language evolution and secure software distribution mean that a faster feature release cycle that encompasses older versions is needed to properly support the latter.
In addition, the core CPython development team have the luxury of dropping support for earlier Python versions well before the rest of the community, as downstream commercial redistributors pick up the task of providing support for those versions to users that still need it, while many third party libraries maintain compatibility with those versions as long as they remain in widespread use.
This means that the current
setup.py install based model for package
installation poses serious difficulties for the development and adoption
of new packaging standards, as, depending on how a project writes their
setup.py file, the installation command (along with other operations)
may end up invoking the standard library’s
As an indicator of how this may cause problems for the broader ecosystem,
consider that the feature set of
distutils in Python 2.6 was frozen
in June 2008 (with the release of Python 2.6b1), while the feature set of
distutils in Python 2.7 was frozen in April 2010 (with the release of
By contrast, using a separate installer application like
ensures that even
setup.py files that invoke
still support the new packaging standards) makes it possible to support
new packaging standards in older versions of Python, just by upgrading
pip (which receives new feature releases roughly every 6 months). The
situation on older versions of Python is further improved by making it
easier for end users to install and upgrade newer build systems like
setuptools or improved PyPI upload utilities like
It is not coincidental that this proposed model of using a separate installer program with more metadata heavy and less active distribution formats matches that used by most operating systems (including Windows since the introduction of the installer service and the MSI file format), as well as many other language specific installers.
For Python 2.6, this compatibility issue is largely limited to various enterprise Linux distributions (and their downstream derivatives). These distributions often have even slower update cycles than CPython, so they offer full support for versions of Python that are considered “security fix only” versions upstream (and sometimes may even be to the point where the core development team no longer support them at all - you can still get commercial support for Python 2.3 if you really need it!).
In practice, the fact that tools like
curl are readily
available on Linux systems, that most users of Python on Linux are
already familiar with the command line, and that most Linux distributions
ship with a default configuration that makes running Python scripts easy,
means that the existing
pip bootstrapping instructions for any *nix
system are already quite straightforward. Even if
pip isn’t provided by
the system package manager, then using
curl to retrieve the
bootstrap script from www.pip-installer.org and then running it is just a
couple of shell commands that can easily be copied and pasted as necessary.
Accordingly, for any version of Python on any *nix system, the need to
pip in older versions isn’t considered a major barrier to
adoption of new packaging standards, since it’s just one more small
speedbump encountered by users of these long term stable releases. For
*nix systems, this PEP’s formal endorsement of
pip as the preferred
default packaging tool is seen as more important than the underlying
technical details involved in making
pip available by default, since
it shifts the nature of the conversation between the developers of
and downstream repackagers of both
pip and CPython.
For Python 2.7, on the other hand, the compatibility issue for adopting new metadata standards is far more widespread, as it affects the python.org binary installers for Windows and Mac OS X, as well as even relatively fast moving *nix platforms.
Firstly, and unlike Python 2.6, Python 2.7 is still a fully supported upstream version, and will remain so until the release of Python 2.7.9 (currently scheduled for May 2015), at which time it is expected to enter the usual “security fix only” mode. That means there are at least another 19 months where Python 2.7 is a deployment target for Python applications that enjoys full upstream support. Even after the core development team switches 2.7 to security release only mode in 2015, Python 2.7 will likely remain a commercially supported legacy target out beyond 2020.
While Python 3 already presents a compelling alternative over Python 2 for new Python applications and deployments without an existing investment in Python 2 and without a dependency on specific Python 2 only third party modules (a set which is getting ever smaller over time), it is going to take longer to create compelling business cases to update existing Python 2.7 based infrastructure to Python 3, especially in situations where the culture of automated testing is weak (or nonexistent), making it difficult to effectively use the available migration utilities.
While this PEP only proposes documentation changes for Python 2.7, once
pip has a Windows installer available, a separate PEP will be created
and submitted proposing the creation and distribution of aggregate installers
for future CPython 2.7 maintenance releases that combine the CPython,
pip and Python Launcher for Windows installers into a single download
(the separate downloads would still remain available - the aggregate
installers would be provided as a convenience, and as a clear indication
of the recommended operating environment for Python in Windows systems).
pip has been chosen as the preferred default installer, as it is an
already popular tool that 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
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
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
yum (which are also designed to handle arbitrary
This PEP proposes that the
Installing Python Modules guide be
updated to officially recommend the use of
pip as the default
installer for Python packages, rather than the current approach of
recommending the direct invocation of the
setup.py install command.
However, to avoid recommending a tool that CPython does not provide, it is
further proposed that the pip package manager be made available by
default when installing CPython 3.4 or later and when creating virtual
environments using the standard library’s
venv module via the
pyvenv command line utility.
To support that end, this PEP proposes the inclusion of an
bootstrapping module in Python 3.4, as well as automatic invocation of that
pyvenv and changes to the way Python installed scripts are
handled on Windows. Using a bootstrap module rather than providing
directly helps to clearly demarcate development responsibilities, and to
avoid inadvertently downgrading
pip when updating CPython.
To provide clear guidance for new users of Python that may not be
starting with the latest release, this PEP also proposes that the
“Installing Python Modules” guides in Python 2.7 and 3.3 be updated to
recommend installing and using
pip, rather than invoking
directly. It does not propose backporting any of the code changes that
are being proposed for Python 3.4.
Finally, 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.
This PEP does not propose making pip (or any dependencies) directly available as part of the standard library. Instead, pip will be a bundled application provided along with CPython for the convenience of Python users, but subject to its own development life cycle and able to be upgraded independently of the core interpreter and standard library.
Explicit bootstrapping mechanism
An additional module called
ensurepip will be added to the standard
library whose purpose is to install pip and any of its dependencies into the
appropriate location (most commonly site-packages). It will expose a
bootstrap() as well as offer direct execution via
python -m ensurepip.
The bootstrap will not contact PyPI, but instead rely on a private copy
of pip stored inside the standard library. Accordingly, only options
related to the installation location will be supported (
It is considered desirable that users be strongly encouraged to use the
latest available version of
pip, in order to take advantage of the
ongoing efforts to improve the security of the PyPI based ecosystem, as
well as benefiting from the efforts to improve the speed, reliability and
flexibility of that ecosystem.
In order to satisfy this goal of providing the most recent version of
pip by default, the private copy of
pip will be updated in CPython
maintenance releases, which should align well with the 6-month cycle used
The design in this PEP has been deliberately chosen to avoid making any
significant changes to the trust model of CPython for end users that do
not subsequently run the command
pip install --upgrade pip.
The installers will contain all the components of a fully functioning
version of Python, including the
pip installer. The installation
process will not require network access, and will not rely on
trusting the security of the network connection established between
pip and the Python package index.
Only users that choose to use
pip to communicate with PyPI will
need to pay attention to the additional security considerations that come
with doing so.
However, the core CPython team will still assist with reviewing and
resolving at least the certificate update management issue currently
requests project (and hence
pip), and may also be
able to offer assistance in resolving other identified security concerns
By including the bootstrap as part of the standard library (rather than solely as a feature of the binary installers), the correct operation of the bootstrap command can be easily tested using the existing CPython buildbot infrastructure rather than adding significantly to the testing burden for the installers themselves.
To ensure there is no need for network access when installing Python or
creating virtual environments, the
ensurepip module will, as an
implementation detail, include a complete private copy of pip and its
dependencies which will be used to extract pip and install it into the target
environment. It is important to stress that this private copy of pip is
only an implementation detail and it should not be relied on or
assumed to exist beyond the public capabilities exposed through the
ensurepip module (and indirectly through
There is not yet a reference
ensurepip implementation. The existing
get-pip.py bootstrap script demonstrates an earlier variation of the
general concept, but the standard library version would take advantage of
the improved distribution capabilities offered by the CPython installers
to include private copies of
setuptools as wheel files
(rather than as embedded base64 encoded data), and would not try to
contact PyPI (instead installing directly from the private wheel files).
Rather than including separate code to handle the bootstrapping, the
ensurepip module will manipulate
sys.path appropriately to allow
the wheel files to be used to install themselves, either into the current
Python installation or into a virtual environment (as determined by the
options passed to the bootstrap command).
It is proposed that the implementation be carried out in five separate steps (all steps after the first two are independent of each other and can be carried out in any order):
- the first step would update the “Installing Python Modules” documentation
to recommend the use of
pipand reference the
pipteam’s instructions for downloading and installing it. This change would be applied to Python 2.7, 3.3, and 3.4.
ensurepipmodule and the private copies of the most recently released versions of pip and setuptools would be added to Python 3.4 and the 3.4 “Installing Python Modules” documentation updated accordingly.
- the CPython Windows installer would be updated to offer the new
pipinstallation option for Python 3.4.
- the CPython Mac OS X installer would be updated to offer the new
pipinstallation option for Python 3.4.
pyvenvcommand would be updated to make use of
ensurepipin Python 3.4
- the PATH handling on Windows would be updated for Python 3.4+
If this PEP is accepted, the proposed time frame for integration of
into the CPython release is as follows:
- as soon as possible after the release of 3.4.0 alpha 4
- Documentation updated and
ensurepipimplemented based on a pre-release version of
- All other proposed functional changes for Python 3.4 implemented,
including the installer updates to invoke
- Documentation updated and
- by November 20th (3 days prior to the scheduled date of 3.4.0 beta 1)
ensurepipupdated to use a
pip1.5 release candidate.
- PEP 101 updated to cover ensuring the bundled version of
pipis up to date.
- by November 24th (scheduled date of 3.4.0 beta 1)
- As with any other new feature, all proposed functional changes for Python 3.4 must be implemented prior to the beta feature freeze.
- by December 29th (1 week prior to the scheduled date of 3.4.0 beta 2)
requestscertificate management issue resolved
ensurepipupdated to the final release of
pip1.5, or a subsequent maintenance release (including a suitably updated vendored copy of
(See PEP 429 for the current official scheduled dates of each release. Dates listed above are accurate as of October 20th, 2013.)
If there is no final or maintenance release of
pip 1.5 with a suitable
updated version of
requests available by one week before the scheduled
Python 3.4 beta 2 release, then implementation of this PEP will
be deferred to Python 3.5. Note that this scenario is considered unlikely -
the tentative date for the
pip 1.5 release is currently December 1st.
In future CPython releases, this kind of coordinated scheduling shouldn’t be
needed: the CPython release manager will be able to just update to the latest
released version of
pip. However, in this case, some fixes are needed in
pip in order to allow the bundling to work correctly, and the
certificate update mechanism for
requests needs to be improved, so the
pip 1.5 release cycle needs to be properly aligned with the CPython 3.4
The proposed CLI is based on a subset of the existing
Usage: python -m ensurepip [options] General Options: -h, --help Show help. -v, --verbose Give more output. Option is additive, and can be used up to 3 times. -V, --version Show the pip version that would be extracted and exit. -q, --quiet Give less output. Installation Options: -U, --upgrade Upgrade pip and dependencies, even if already installed --user Install using the user scheme. --root <dir> Install everything relative to this alternate root directory.
In most cases, end users won’t need to use this CLI directly, as
should have been installed automatically when installing Python or when
creating a virtual environment. However, it is formally documented as a
public interface to support at least these known use cases:
- Windows and Mac OS X installations where the “Install pip” option was not chosen during installation
- any installation where the user previously ran “pip uninstall pip”
Users that want to retrieve the latest version from PyPI, or otherwise
need more flexibility, can then invoke the extracted
Proposed module API
ensurepip module API consists of the following two
def version(): """ Returns a string specifying the bundled version of pip. """ def bootstrap(root=None, upgrade=False, user=False, verbosity=0): """ Bootstrap pip into the current Python installation (or the given root directory). """
Invocation from the CPython installers
The CPython Windows and Mac OS X installers will each gain a new option:
- Install pip (the default Python package management utility)?
This option will be checked by default.
If the option is checked, then the installer will invoke the following command with the just installed Python:
python -m ensurepip --upgrade
This ensures that, by default, installing or updating CPython will ensure
that the installed version of pip is at least as recent as the one included
with that version of CPython. If a newer version of pip has already been
python -m ensurepip --upgrade will simply return without
Installing from source
Just as the prebuilt binary installers will be updated to run
python -m ensurepip by default, a similar change will be made to the
make install and
make altinstall commands of the source
distribution. The directory settings in the
sysconfig module should
pip components are automatically installed to the expected
ensurepip itself (including the private copy of
pip and its
dependencies) will always be installed normally (as it is a regular
part of the standard library), but an option will be provided to skip
the invocation of
This means that even installing from source will provide
pip by default,
but redistributors provide
pip by other means (or not providing it at
all) will still be able to opt out of installing it using
Changes to virtual environments
Python 3.3 included a standard library approach to virtual Python environments
venv module. Since its 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
To handle cases where a user does not wish to have pip bootstrapped into
their virtual environment a
--without-pip option will be
venv.create APIs will be updated to accept
one new parameter:
with_pip (defaulting to
The new default for the module API is chosen for backwards compatibility
with the current behaviour (as it is assumed that most invocation of the
venv module happens through third part tools that likely will not
pip installed without explicitly requesting it), while the
default for the command line interface is chosen to try to ensure
is available in most virtual environments without additional action on the
part of the end user.
As this change will only benefit Python 3.4 and later versions, the
virtualenv project will still be needed to obtain a
consistent cross-version experience in Python 3.3 and 2.7.
The “Installing Python Modules” section of the standard library
documentation in Python 2.7, 3.3 and 3.4 will be updated to recommend
the use of the
pip installer, either provided by default in Python 3.4
or retrieved and installed by the user in Python 2.7 or 3.3. 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.
In Python 3.4, the
venv documentation will also be
updated to reference the revised module installation guide.
The existing content of the module installation guide will be retained in all versions, but under a new “Invoking distutils directly” subsection.
Bundling CA certificates with CPython
ensurepip implementation will include the
pip CA bundle along
with the rest of
pip. This means CPython effectively includes
a CA bundle that is used solely by
pip after it has been extracted.
This is considered preferable to relying solely on the system
certificate stores, 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 current
when Python 3.4.0 is released).
This PEP proposes that, if pip still requires it as a dependency,
ensurepip will include a private copy of
setuptools (in addition
to the private copy of
python -m ensurepip will then
install the private copy in addition to installing
However, this behavior 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
The private copy of
setuptools will be removed from
once it is no longer needed. This is likely to be at the point when
get-pip.py stops installing
setuptools by default.
As long as setuptools is needed, it will be a completely unmodified copy of
the latest upstream setuptools release, including the
script if the upstream setuptools continues to include it. The installation
easy_install along with
pip isn’t considered desirable, but
installing a broken setuptools would be worse. This problem will
naturally resolve itself once the
pip developers have managed to
eliminate their dependency on
setuptools and the private copy of
setuptools can be removed entirely from CPython.
Updating the private copy of pip
In order to keep up with evolutions in packaging as well as providing users
with as recent version a possible the
ensurepip module will be
regularly updated to the latest versions of everything it bootstraps.
After each new
pip release, and again during the preparation for any
release of Python (including feature releases), a script, provided as part
of the implementation for this PEP, will be run to ensure the private
copies stored in the CPython source repository have been updated to the
Updating the ensurepip module API and CLI
ensurepip module API and CLI
will be governed by the normal rules for the standard library: no
new features are permitted in maintenance releases.
However, the embedded components may be updated as noted above, so
pip may offer additional functionality in maintenance
No changes are proposed to the CPython uninstallation process by this PEP. The bootstrapped pip will be installed the same way as any other pip installed packages, and will be handled in the same way as any other post-install additions to the Python environment.
At least on Windows, that means the bootstrapped files will be left behind after uninstallation, since those files won’t be associated with the Python MSI installer.
While the case can be made for the CPython installers clearing out these directories automatically, changing that behaviour is considered outside the scope of this PEP.
Script Execution on Windows
While the Windows installer was updated in Python 3.3 to optionally
python available on the PATH, no such change was made to
include the script installation directory returned by
Accordingly, in addition to adding the option to extract and install
during installation, this PEP proposes that the Windows installer in
Python 3.4 and later be updated to also add the path returned by
sysconfig.get_path("scripts") to the Windows PATH when the PATH
modification option is enabled during installation
Note that this change will only be available in Python 3.4 and later.
This means that, for Python 3.3, the most reliable way to invoke pip globally
on Windows (without tinkering manually with PATH) will still remain
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
works because Python 3.3 provides the Python Launcher for
Windows (and the associated
py command) by default.
For Python 2.7 and 3.2, the most reliable mechanism will be to install the
Python Launcher for Windows using the standalone installer and then use
py -m pip as noted above.
Adding the scripts directory to the system PATH will mean that
works reliably in the “only one Python installation on the system PATH”
py -m pip,
pipX.Y needed only to select a
non-default version in the parallel installation case (and outside a virtual
environment). This change should also make the
pyvenv command substantially
easier to invoke on Windows, along with all scripts installed by
easy_install and similar tools.
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
Recommendations for Downstream Distributors
A common source of Python installations are through downstream distributors such as the various Linux Distributions   , OSX package managers   , and commercial Python redistributors   . In order to provide a consistent, user-friendly experience to all users of Python regardless of how they obtained Python this PEP recommends and asks that downstream distributors:
- Ensure that whenever Python is installed
pipis either installed or is otherwise made readily available to end users.
- For redistributors using binary installers, this may take the form of
optionally executing the
ensurepipbootstrap during installation, similar to the CPython installers.
- For redistributors using package management systems, it may take the form of separate packages with dependencies on each other so that installing the Python package installs the pip package and installing the pip package installs the Python package.
- Another reasonable way to implement this is to package pip separately but
ensure that there is some sort of global hook that will recommend
installing the separate pip package when a user executes
pipwithout it being installed. Systems that choose this option should ensure that the
ensurepipmodule still installs pip directly when invoked inside a virtual environment, but may modify the module in the system Python installation to redirect to the platform provided mechanism when installing
- For redistributors using binary installers, this may take the form of optionally executing the
- Even if pip is made available globally by other means, do not remove the
ensurepipmodule in Python 3.4 or later.
ensurepipwill be required for automatic installation of pip into virtual environments by the
- This is similar to the existing
virtualenvpackage for which many downstream distributors have already made exception to the common “debundling” policy.
- This does mean that if
pipneeds to be updated due to a security issue, so does the private copy in the
- However, altering the private copy of pip to remove the embedded CA certificate bundle and rely on the system CA bundle instead is a reasonable change.
- Ensure that all features of this PEP continue to work with any modifications
made to the redistributed version of Python.
- Checking the version of pip that will be bootstrapped using
python -m ensurepip --versionor
- Installation of pip into a global or virtual python environment using
python -m ensurepipor
pip install --upgrade pipin a global installation should not affect any already created virtual environments (but is permitted to affect future virtual environments, even though it will not do so when using the standard implementation of
pip install --upgrade pipin a virtual environment should not affect the global installation.
- Checking the version of pip that will be bootstrapped using
- Migrate build systems to utilize pip and Wheel
and avoid directly invoking
- This will help ensure a smoother and more timely migration to improved metadata formats as the Python packaging ecosystem continues to evolve.
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
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 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 already placed in the Python Packaging Authority as
the authors and maintainers of
and other related projects.
The public API and CLI of the
ensurepip 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 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.
Any security update that affects the
ensurepip module will be shared
prior to release with the Python Security Response Team
(email@example.com). The PSRT will then decide if the reported issue
warrants a security release of CPython with an updated private copy of
pip is currently licensed as 1 Clause BSD, and it contains code taken
from other projects. Additionally this PEP will include setuptools until
such time as pip no longer requires it. The licenses for these appear in
the table below.
|six||1 Clause BSD|
|html5lib||1 Clause BSD|
|colorama||3 Clause BSD|
|Mozilla CA Bundle||LGPL|
All of these licenses should be compatible with the PSF license. Additionally it is unclear if a CA Bundle is copyrightable material and thus if it needs or can be licensed at all.
Appendix: Rejected Proposals
Changing the name of the scripts directory on Windows
Earlier versions of this PEP proposed changing the name of the script
installation directory on Windows from “Scripts” to “bin” in order to
improve the cross-platform consistency of the virtual environments created
However, Paul Moore determined that this change was likely backwards incompatible with cross-version Windows installers created with previous versions of Python, so the change has been removed from this PEP .
Including ensurepip in Python 2.7, and 3.3
Earlier versions of this PEP made the case that the challenges of getting
pip bootstrapped for new users posed a significant enough barrier to
Python’s future growth that it justified adding
ensurepip as a new
feature in the upcoming Python 2.7 and 3.3 maintenance releases.
While the proposal to provide
pip with Python 3.4 was universally
popular, this part of the proposal was highly controversial and ultimately
rejected by MvL as BDFL-Delegate.
Accordingly, the proposal to backport
ensurepip to Python 2.7 and 3.3
has been removed from this PEP in favour of creating a Windows installer
pip and a possible future PEP suggesting creation of an aggregate
installer for Python 2.7 that combines CPython 2.7,
pip and the Python
Launcher for Windows.
Automatically contacting PyPI when bootstrapping pip
Earlier versions of this PEP called the bootstrapping module
defaulted to downloading and installing
pip from PyPI, with the private
copy used only as a fallback option or when explicitly requested.
This resulted in several complex edge cases, along with difficulties in
defining a clean API and CLI for the bootstrap module. It also significantly
altered the default trust model for the binary installers published on
python.org, as end users would need to explicitly opt-out of trusting
the security of the PyPI ecosystem (rather than opting in to it by
pip following installation).
As a result, the PEP was simplified to the current design, where the
bootstrapping always uses the private copy of
pip. Contacting PyPI
is now always an explicit separate step, with direct access to the full
Removing the implicit attempt to access PyPI also made it feasible to
ensurepip by default when installing from a custom source build.
PEP 439, 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.
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 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
end user facing problems with not having pip present by default. This has been
rejected because we’ve learned, through the inclusion and history of
distutils in the standard library, that losing the ability to update the
packaging tools independently can leave the tooling in a state of constant
limbo. Making it unable to ever reasonably evolve in a time frame that actually
affects users as any new features will not be available to the general
population for years.
Allowing the packaging tools to progress separately from the Python release and adoption schedules allows the improvements to be used by all members 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
The approach described in this PEP also avoids some technical issues
related to handling 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
ensurepip bootstrap module).
Finally, the separate bootstrapping step means it is also easy to avoid
pip at all if end users so desire. This is often the case
if integrators are using system packages to handle installation of
components written in multiple languages using a common set of tools.
Defaulting to –user installation
Some consideration was given to bootstrapping pip into the per-user site-packages directory by default. However, this behavior would be surprising (as it differs from the default behavior 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).
This document has been placed in the public domain.
Last modified: 2022-07-02 06:19:33 GMT