Vendored libraries MUST not be modified except as required to successfully vendor them.
Vendored libraries MUST be released copies of libraries available on PyPI.
Vendored libraries MUST be available under a license that allows them to be integrated into
pip, which is released under the MIT license.
Vendored libraries MUST be accompanied with LICENSE files.
The versions of libraries vendored in pip MUST be reflected in
Vendored libraries MUST function without any build steps such as
2to3or compilation of C code, practically this limits to single source 2.x/3.x and pure Python.
Any modifications made to libraries MUST be noted in
pip/_vendor/README.rstand their corresponding patches MUST be included
Vendored libraries should have corresponding
Historically pip has not had any dependencies except for
choosing instead to implement any functionality it needed to prevent needing
a dependency. However, starting with pip 1.5, we began to replace code that was
implemented inside of pip with reusable libraries from PyPI. This brought the
typical benefits of reusing libraries instead of reinventing the wheel like
higher quality and more battle tested code, centralization of bug fixes
(particularly security sensitive ones), and better/more features for less work.
However, there are several issues with having dependencies in the traditional
install_requires) for pip. These issues are:
When pip depends on another library to function then if for whatever reason that library either isn’t installed or an incompatible version is installed then pip ceases to function. This is of course true for all Python applications, however for every application except for pip the way you fix it is by re-running pip. Obviously, when pip can’t run, you can’t use pip to fix pip, so you’re left having to manually resolve dependencies and installing them by hand.
- Making other libraries uninstallable
One of pip’s current dependencies is the
requestslibrary, for which pip requires a fairly recent version to run. If pip depended on
requestsin the traditional manner, then we’d either have to maintain compatibility with every
requestsversion that has ever existed (and ever will), OR allow pip to render certain versions of
requestsuninstallable. (The second issue, although technically true for any Python application, is magnified by pip’s ubiquity; pip is installed by default in Python, in
pyvenv, and in
This might seem puzzling at first glance, since vendoring has a tendency to complicate updating dependencies for security updates, and that holds true for pip. However, given the other reasons for avoiding dependencies, the alternative is for pip to reinvent the wheel itself. This is what pip did historically. It forced pip to re-implement its own HTTPS verification routines as a workaround for the Python standard library’s lack of SSL validation, which resulted in similar bugs in the validation routine in
urllib3, except that they had to be discovered and fixed independently. Even though we’re vendoring, reusing libraries keeps pip more secure by relying on the great work of our dependencies, and allowing for faster, easier security fixes by simply pulling in newer versions of dependencies.
Currently most popular methods of installing pip rely on pip’s self-contained nature to install pip itself. These tools work by bundling a copy of pip, adding it to
sys.path, and then executing that copy of pip. This is done instead of implementing a “mini installer” (to reduce duplication); pip already knows how to install a Python package, and is far more battle-tested than any “mini installer” could ever possibly be.
Many downstream redistributors have policies against this kind of bundling, and
instead opt to patch the software they distribute to debundle it and make it
rely on the global versions of the software that they already have packaged
(which may have its own patches applied to it). We (the pip team) would prefer
it if pip was not debundled in this manner due to the above reasons and
instead we would prefer it if pip would be left intact as it is now. The one
exception to this, is it is acceptable to remove the
pip/_vendor/requests/cacert.pem file provided you ensure that the
ssl.get_default_verify_paths().cafile API returns the correct CA bundle for
your system. This will ensure that pip will use your system provided CA bundle
instead of the copy bundled with pip.
In the longer term, if someone has a portable solution to the above problems, other than the bundling method we currently use, that doesn’t add additional problems that are unreasonable then we would be happy to consider, and possibly switch to said method. This solution must function correctly across all of the situation that we expect pip to be used and not mandate some external mechanism such as OS packages.
setuptoolsis completely stripped to only keep
pkg_resourceshas been modified to import its dependencies from
pip._vendor, and to use the vendored copy of
packaginghas been modified to import its dependencies from
html5libhas been modified to import six from
pip._vendor, to prefer importing from
collectionsand does not import
xml.etree.cElementTreeon Python 3.
CacheControlhas been modified to import its dependencies from
requestshas been modified to import its other dependencies from
pip._vendorand to not load
simplejson(all platforms) and
platformdirshas been modified to import its submodules from
Vendoring is automated via the vendoring tool from the content of
pip/_vendor/vendor.txt and the different patches in
Launch it via
vendoring sync . -v (requires
As mentioned in the rationale, we, the pip team, would prefer it if pip was not
debundled (other than optionally
pip/_vendor/requests/cacert.pem) and that
pip was left intact. However, if you insist on doing so, we have a
semi-supported method (that we don’t test in our CI) and requires a bit of
extra work on your end in order to solve the problems described above.
Delete everything in
Generate wheels for each of pip’s dependencies (and any of their dependencies) using your patched copies of these libraries. These must be placed somewhere on the filesystem that pip can access (
pip/_vendoris the default assumption).
pip/_vendor/__init__.pyso that the
Upon installation, the
INSTALLERfile in pip’s own
dist-infodirectory should be set to something other than
pip, so that pip can detect that it wasn’t installed using itself.
(optional) If you’ve placed the wheels in a location other than
pip/_vendor/, then modify
pip/_vendor/__init__.pyso that the
WHEEL_DIRvariable points to the location you’ve placed them.
(optional) Update the
pip_self_version_checklogic to use the appropriate logic for determining the latest available version of pip and prompt the user with the correct upgrade message.
Note that partial debundling is NOT supported. You need to prepare wheels for all dependencies for successful debundling.