Как обновить python в windows через pip

User Guide

Running pip

pip is a command line program. When you install pip, a pip command is added
to your system, which can be run from the command prompt as follows:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip <pip arguments>

   ``python -m pip`` executes pip using the Python interpreter you
   specified as python. So ``/usr/bin/python3.7 -m pip`` means
   you are executing pip for your interpreter located at ``/usr/bin/python3.7``.

.. tab:: Windows

   .. code-block:: shell

      py -m pip <pip arguments>

   ``py -m pip`` executes pip using the latest Python interpreter you
   have installed. For more details, read the `Python Windows launcher`_ docs.

Installing Packages

pip supports installing from PyPI, version control, local projects, and
directly from distribution files.

The most common scenario is to install from PyPI using :ref:`Requirement
Specifiers`

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install SomePackage            # latest version
      python -m pip install SomePackage==1.0.4     # specific version
      python -m pip install 'SomePackage>=1.0.4'     # minimum version

.. tab:: Windows

   .. code-block:: shell

      py -m pip install SomePackage            # latest version
      py -m pip install SomePackage==1.0.4     # specific version
      py -m pip install 'SomePackage>=1.0.4'   # minimum version

For more information and examples, see the :ref:`pip install` reference.

Basic Authentication Credentials

This is now covered in :doc:`topics/authentication`.

netrc Support

This is now covered in :doc:`topics/authentication`.

Keyring Support

This is now covered in :doc:`topics/authentication`.

Using a Proxy Server

When installing packages from PyPI, pip requires internet access, which
in many corporate environments requires an outbound HTTP proxy server.

pip can be configured to connect through a proxy server in various ways:

• using the --proxy command-line option to specify a proxy in the form
  scheme://[user:passwd@]proxy.server:port
• using proxy in a :ref:`config-file`
• by setting the standard environment-variables http_proxy, https_proxy
  and no_proxy.
• using the environment variable PIP_USER_AGENT_USER_DATA to include
  a JSON-encoded string in the user-agent variable used in pip’s requests.

Requirements Files

«Requirements files» are files containing a list of items to be
installed using :ref:`pip install` like so:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install -r requirements.txt

.. tab:: Windows

   .. code-block:: shell

      py -m pip install -r requirements.txt

Details on the format of the files are here: :ref:`requirements-file-format`.

Logically, a Requirements file is just a list of :ref:`pip install` arguments
placed in a file. Note that you should not rely on the items in the file being
installed by pip in any particular order.

In practice, there are 4 common uses of Requirements files:

1. Requirements files are used to hold the result from :ref:`pip freeze` for the
   purpose of achieving :doc:`topics/repeatable-installs`. In
   this case, your requirement file contains a pinned version of everything that
   was installed when pip freeze was run.

   .. tab:: Unix/macOS
   
      .. code-block:: shell
   
         python -m pip freeze > requirements.txt
         python -m pip install -r requirements.txt
   
   

   .. tab:: Windows
   
      .. code-block:: shell
   
         py -m pip freeze > requirements.txt
         py -m pip install -r requirements.txt
   
   

2. Requirements files are used to force pip to properly resolve dependencies.
   pip 20.2 and earlier doesn’t have true dependency resolution, but instead simply uses the first
   specification it finds for a project. E.g. if pkg1 requires
   pkg3>=1.0 and pkg2 requires pkg3>=1.0,<=2.0, and if pkg1 is
   resolved first, pip will only use pkg3>=1.0, and could easily end up
   installing a version of pkg3 that conflicts with the needs of pkg2.
   To solve this problem, you can place pkg3>=1.0,<=2.0 (i.e. the correct
   specification) into your requirements file directly along with the other top
   level requirements. Like so:

   pkg1
   pkg2
   pkg3>=1.0,<=2.0
   

3. Requirements files are used to force pip to install an alternate version of a
   sub-dependency. For example, suppose ProjectA in your requirements file
   requires ProjectB, but the latest version (v1.3) has a bug, you can force
   pip to accept earlier versions like so:

   ProjectA
   ProjectB<1.3
   

4. Requirements files are used to override a dependency with a local patch that
   lives in version control. For example, suppose a dependency
   SomeDependency from PyPI has a bug, and you can’t wait for an upstream
   fix.
   You could clone/copy the src, make the fix, and place it in VCS with the tag
   sometag. You’d reference it in your requirements file with a line like
   so:

   git+https://myvcs.com/some_dependency@sometag#egg=SomeDependency
   

   If SomeDependency was previously a top-level requirement in your
   requirements file, then replace that line with the new line. If
   SomeDependency is a sub-dependency, then add the new line.

It’s important to be clear that pip determines package dependencies using
install_requires metadata,
not by discovering requirements.txt files embedded in projects.

See also:

• :ref:`requirements-file-format`
• :ref:`pip freeze`
• «setup.py vs requirements.txt» (an article by Donald Stufft)

Constraints Files

Constraints files are requirements files that only control which version of a
requirement is installed, not whether it is installed or not. Their syntax and
contents is a subset of :ref:`Requirements Files`, with several kinds of syntax
not allowed: constraints must have a name, they cannot be editable, and they
cannot specify extras. In terms of semantics, there is one key difference:
Including a package in a constraints file does not trigger installation of the
package.

Use a constraints file like so:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install -c constraints.txt

.. tab:: Windows

   .. code-block:: shell

      py -m pip install -c constraints.txt

Constraints files are used for exactly the same reason as requirements files
when you don’t know exactly what things you want to install. For instance, say
that the «helloworld» package doesn’t work in your environment, so you have a
local patched version. Some things you install depend on «helloworld», and some
don’t.

One way to ensure that the patched version is used consistently is to
manually audit the dependencies of everything you install, and if «helloworld»
is present, write a requirements file to use when installing that thing.

Constraints files offer a better way: write a single constraints file for your
organisation and use that everywhere. If the thing being installed requires
«helloworld» to be installed, your fixed version specified in your constraints
file will be used.

Constraints file support was added in pip 7.1. In :ref:`Resolver
changes 2020` we did a fairly comprehensive overhaul, removing several
undocumented and unsupported quirks from the previous implementation,
and stripped constraints files down to being purely a way to specify
global (version) limits for packages.

Installing from Wheels

«Wheel» is a built, archive format that can greatly speed installation compared
to building and installing from source archives. For more information, see the
Wheel docs , PEP 427, and PEP 425.

pip prefers Wheels where they are available. To disable this, use the
:ref:`—no-binary <install_—no-binary>` flag for :ref:`pip install`.

If no satisfactory wheels are found, pip will default to finding source
archives.

To install directly from a wheel archive:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install SomePackage-1.0-py2.py3-none-any.whl

.. tab:: Windows

   .. code-block:: shell

      py -m pip install SomePackage-1.0-py2.py3-none-any.whl

To include optional dependencies provided in the provides_extras
metadata in the wheel, you must add quotes around the install target
name:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install './somepackage-1.0-py2.py3-none-any.whl[my-extras]'

.. tab:: Windows

   .. code-block:: shell

      py -m pip install './somepackage-1.0-py2.py3-none-any.whl[my-extras]'

For the cases where wheels are not available, pip offers :ref:`pip wheel` as a
convenience, to build wheels for all your requirements and dependencies.

:ref:`pip wheel` requires the wheel package to be installed, which provides the
«bdist_wheel» setuptools extension that it uses.

To build wheels for your requirements and all their dependencies to a local
directory:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install wheel
      python -m pip wheel --wheel-dir=/local/wheels -r requirements.txt

.. tab:: Windows

   .. code-block:: shell

      py -m pip install wheel
      py -m pip wheel --wheel-dir=/local/wheels -r requirements.txt

And then to install those requirements just using your local directory of
wheels (and not from PyPI):

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install --no-index --find-links=/local/wheels -r requirements.txt

.. tab:: Windows

   .. code-block:: shell

      py -m pip install --no-index --find-links=/local/wheels -r requirements.txt

Uninstalling Packages

pip is able to uninstall most packages like so:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip uninstall SomePackage

.. tab:: Windows

   .. code-block:: shell

      py -m pip uninstall SomePackage

pip also performs an automatic uninstall of an old version of a package
before upgrading to a newer version.

For more information and examples, see the :ref:`pip uninstall` reference.

Listing Packages

To list installed packages:

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip list
      docutils (0.9.1)
      Jinja2 (2.6)
      Pygments (1.5)
      Sphinx (1.1.2)

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip list
      docutils (0.9.1)
      Jinja2 (2.6)
      Pygments (1.5)
      Sphinx (1.1.2)

To list outdated packages, and show the latest version available:

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip list --outdated
      docutils (Current: 0.9.1 Latest: 0.10)
      Sphinx (Current: 1.1.2 Latest: 1.1.3)

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip list --outdated
      docutils (Current: 0.9.1 Latest: 0.10)
      Sphinx (Current: 1.1.2 Latest: 1.1.3)

To show details about an installed package:

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip show sphinx
      ---
      Name: Sphinx
      Version: 1.1.3
      Location: /my/env/lib/pythonx.x/site-packages
      Requires: Pygments, Jinja2, docutils

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip show sphinx
      ---
      Name: Sphinx
      Version: 1.1.3
      Location: /my/env/lib/pythonx.x/site-packages
      Requires: Pygments, Jinja2, docutils

For more information and examples, see the :ref:`pip list` and :ref:`pip show`
reference pages.

Searching for Packages

pip can search PyPI for packages using the pip search
command:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip search "query"

.. tab:: Windows

   .. code-block:: shell

      py -m pip search "query"

The query will be used to search the names and summaries of all
packages.

For more information and examples, see the :ref:`pip search` reference.

Configuration

This is now covered in :doc:`topics/configuration`.

Config file

This is now covered in :doc:`topics/configuration`.

Environment Variables

This is now covered in :doc:`topics/configuration`.

Config Precedence

This is now covered in :doc:`topics/configuration`.

Command Completion

pip comes with support for command line completion in bash, zsh and fish.

To setup for bash:

python -m pip completion --bash >> ~/.profile

To setup for zsh:

python -m pip completion --zsh >> ~/.zprofile

To setup for fish:

python -m pip completion --fish > ~/.config/fish/completions/pip.fish

To setup for powershell:

python -m pip completion --powershell | Out-File -Encoding default -Append $PROFILE

Alternatively, you can use the result of the completion command directly
with the eval function of your shell, e.g. by adding the following to your
startup file:

eval "`pip completion --bash`"

Installing from local packages

In some cases, you may want to install from local packages only, with no traffic
to PyPI.

First, download the archives that fulfill your requirements:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip download --destination-directory DIR -r requirements.txt

.. tab:: Windows

   .. code-block:: shell

      py -m pip download --destination-directory DIR -r requirements.txt

Note that pip download will look in your wheel cache first, before
trying to download from PyPI. If you’ve never installed your requirements
before, you won’t have a wheel cache for those items. In that case, if some of
your requirements don’t come as wheels from PyPI, and you want wheels, then run
this instead:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip wheel --wheel-dir DIR -r requirements.txt

.. tab:: Windows

   .. code-block:: shell

      py -m pip wheel --wheel-dir DIR -r requirements.txt

Then, to install from local only, you’ll be using :ref:`—find-links
<install_—find-links>` and :ref:`—no-index <install_—no-index>` like so:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install --no-index --find-links=DIR -r requirements.txt

.. tab:: Windows

   .. code-block:: shell

      py -m pip install --no-index --find-links=DIR -r requirements.txt

«Only if needed» Recursive Upgrade

pip install --upgrade now has a --upgrade-strategy option which
controls how pip handles upgrading of dependencies. There are 2 upgrade
strategies supported:

• eager: upgrades all dependencies regardless of whether they still satisfy
  the new parent requirements
• only-if-needed: upgrades a dependency only if it does not satisfy the new
  parent requirements

The default strategy is only-if-needed. This was changed in pip 10.0 due to
the breaking nature of eager when upgrading conflicting dependencies.

It is important to note that --upgrade affects direct requirements (e.g.
those specified on the command-line or via a requirements file) while
--upgrade-strategy affects indirect requirements (dependencies of direct
requirements).

As an example, say SomePackage has a dependency, SomeDependency, and
both of them are already installed but are not the latest available versions:

• pip install SomePackage: will not upgrade the existing SomePackage or
  SomeDependency.
• pip install --upgrade SomePackage: will upgrade SomePackage, but not
  SomeDependency (unless a minimum requirement is not met).
• pip install --upgrade SomePackage --upgrade-strategy=eager: upgrades both
  SomePackage and SomeDependency.

As an historic note, an earlier «fix» for getting the only-if-needed
behaviour was:

.. tab:: Unix/macOS

   .. code-block:: shell

      python -m pip install --upgrade --no-deps SomePackage
      python -m pip install SomePackage

.. tab:: Windows

   .. code-block:: shell

      py -m pip install --upgrade --no-deps SomePackage
      py -m pip install SomePackage

A proposal for an upgrade-all command is being considered as a safer
alternative to the behaviour of eager upgrading.

User Installs

With Python 2.6 came the «user scheme» for installation,
which means that all Python distributions support an alternative install
location that is specific to a user. The default location for each OS is
explained in the python documentation for the site.USER_BASE variable.
This mode of installation can be turned on by specifying the :ref:`—user
<install_—user>` option to pip install.

Moreover, the «user scheme» can be customized by setting the
PYTHONUSERBASE environment variable, which updates the value of
site.USER_BASE.

To install «SomePackage» into an environment with site.USER_BASE customized to
‘/myappenv’, do the following:

.. tab:: Unix/macOS

   .. code-block:: shell

      export PYTHONUSERBASE=/myappenv
      python -m pip install --user SomePackage

.. tab:: Windows

   .. code-block:: shell

      set PYTHONUSERBASE=c:/myappenv
      py -m pip install --user SomePackage

pip install --user follows four rules:

1. When globally installed packages are on the python path, and they conflict
   with the installation requirements, they are ignored, and not
   uninstalled.
2. When globally installed packages are on the python path, and they satisfy
   the installation requirements, pip does nothing, and reports that
   requirement is satisfied (similar to how global packages can satisfy
   requirements when installing packages in a --system-site-packages
   virtualenv).
3. pip will not perform a --user install in a --no-site-packages
   virtualenv (i.e. the default kind of virtualenv), due to the user site not
   being on the python path. The installation would be pointless.
4. In a --system-site-packages virtualenv, pip will not install a package
   that conflicts with a package in the virtualenv site-packages. The —user
   installation would lack sys.path precedence and be pointless.

To make the rules clearer, here are some examples:

From within a --no-site-packages virtualenv (i.e. the default kind):

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip install --user SomePackage
      Can not perform a '--user' install. User site-packages are not visible in this virtualenv.

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip install --user SomePackage
      Can not perform a '--user' install. User site-packages are not visible in this virtualenv.

From within a --system-site-packages virtualenv where SomePackage==0.3
is already installed in the virtualenv:

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip install --user SomePackage==0.4
      Will not install to the user site because it will lack sys.path precedence

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip install --user SomePackage==0.4
      Will not install to the user site because it will lack sys.path precedence

From within a real python, where SomePackage is not installed globally:

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip install --user SomePackage
      [...]
      Successfully installed SomePackage

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip install --user SomePackage
      [...]
      Successfully installed SomePackage

From within a real python, where SomePackage is installed globally, but
is not the latest version:

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip install --user SomePackage
      [...]
      Requirement already satisfied (use --upgrade to upgrade)
      $ python -m pip install --user --upgrade SomePackage
      [...]
      Successfully installed SomePackage

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip install --user SomePackage
      [...]
      Requirement already satisfied (use --upgrade to upgrade)
      C:> py -m pip install --user --upgrade SomePackage
      [...]
      Successfully installed SomePackage

From within a real python, where SomePackage is installed globally, and
is the latest version:

.. tab:: Unix/macOS

   .. code-block:: console

      $ python -m pip install --user SomePackage
      [...]
      Requirement already satisfied (use --upgrade to upgrade)
      $ python -m pip install --user --upgrade SomePackage
      [...]
      Requirement already up-to-date: SomePackage
      # force the install
      $ python -m pip install --user --ignore-installed SomePackage
      [...]
      Successfully installed SomePackage

.. tab:: Windows

   .. code-block:: console

      C:> py -m pip install --user SomePackage
      [...]
      Requirement already satisfied (use --upgrade to upgrade)
      C:> py -m pip install --user --upgrade SomePackage
      [...]
      Requirement already up-to-date: SomePackage
      # force the install
      C:> py -m pip install --user --ignore-installed SomePackage
      [...]
      Successfully installed SomePackage

Ensuring Repeatability

This is now covered in :doc:`../topics/repeatable-installs`.

Fixing conflicting dependencies

This is now covered in :doc:`../topics/dependency-resolution`.

Using pip from your program

As noted previously, pip is a command line program. While it is implemented in
Python, and so is available from your Python code via import pip, you must
not use pip’s internal APIs in this way. There are a number of reasons for this:

1. The pip code assumes that it is in sole control of the global state of the
   program.
   pip manages things like the logging system configuration, or the values of
   the standard IO streams, without considering the possibility that user code
   might be affected.
2. pip’s code is not thread safe. If you were to run pip in a thread, there
   is no guarantee that either your code or pip’s would work as you expect.
3. pip assumes that once it has finished its work, the process will terminate.
   It doesn’t need to handle the possibility that other code will continue to
   run after that point, so (for example) calling pip twice in the same process
   is likely to have issues.

This does not mean that the pip developers are opposed in principle to the idea
that pip could be used as a library — it’s just that this isn’t how it was
written, and it would be a lot of work to redesign the internals for use as a
library, handling all of the above issues, and designing a usable, robust and
stable API that we could guarantee would remain available across multiple
releases of pip. And we simply don’t currently have the resources to even
consider such a task.

What this means in practice is that everything inside of pip is considered an
implementation detail. Even the fact that the import name is pip is subject
to change without notice. While we do try not to break things as much as
possible, all the internal APIs can change at any time, for any reason. It also
means that we generally won’t fix issues that are a result of using pip in an
unsupported way.

It should also be noted that installing packages into sys.path in a running
Python process is something that should only be done with care. The import
system caches certain data, and installing new packages while a program is
running may not always behave as expected. In practice, there is rarely an
issue, but it is something to be aware of.

Having said all of the above, it is worth covering the options available if you
decide that you do want to run pip from within your program. The most reliable
approach, and the one that is fully supported, is to run pip in a subprocess.
This is easily done using the standard subprocess module:

subprocess.check_call([sys.executable, '-m', 'pip', 'install', 'my_package'])

If you want to process the output further, use one of the other APIs in the module.
We are using freeze here which outputs installed packages in requirements format.:

reqs = subprocess.check_output([sys.executable, '-m', 'pip', 'freeze'])

If you don’t want to use pip’s command line functionality, but are rather
trying to implement code that works with Python packages, their metadata, or
PyPI, then you should consider other, supported, packages that offer this type
of ability. Some examples that you could consider include:

• packaging — Utilities to work with standard package metadata (versions,
  requirements, etc.)
• setuptools (specifically pkg_resources) — Functions for querying what
  packages the user has installed on their system.
• distlib — Packaging and distribution utilities (including functions for
  interacting with PyPI).

Changes to the pip dependency resolver in 20.3 (2020)

pip 20.3 has a new dependency resolver, on by default for Python 3
users. (pip 20.1 and 20.2 included pre-release versions of the new
dependency resolver, hidden behind optional user flags.) Read below
for a migration guide, how to invoke the legacy resolver, and the
deprecation timeline. We also made a two-minute video explanation
you can watch.

We will continue to improve the pip dependency resolver in response to
testers’ feedback. Please give us feedback through the resolver
testing survey.

Watch out for

The big change in this release is to the pip dependency resolver
within pip.

Computers need to know the right order to install pieces of software
(«to install x, you need to install y first»). So, when Python
programmers share software as packages, they have to precisely describe
those installation prerequisites, and pip needs to navigate tricky
situations where it’s getting conflicting instructions. This new
dependency resolver will make pip better at handling that tricky
logic, and make pip easier for you to use and troubleshoot.

The most significant changes to the resolver are:

• It will reduce inconsistency: it will no longer install a
  combination of packages that is mutually inconsistent. In older
  versions of pip, it is possible for pip to install a package which
  does not satisfy the declared requirements of another installed
  package. For example, in pip 20.0, pip install "six<1.12"
"virtualenv==20.0.2" does the wrong thing, “successfully” installing
  six==1.11, even though virtualenv==20.0.2 requires
  six>=1.12.0,<2 (defined here).
  The new resolver, instead, outright rejects installing anything if it
  gets that input.
• It will be stricter — if you ask pip to install two packages with
  incompatible requirements, it will refuse (rather than installing a
  broken combination, like it did in previous versions).

So, if you have been using workarounds to force pip to deal with
incompatible or inconsistent requirements combinations, now’s a good
time to fix the underlying problem in the packages, because pip will
be stricter from here on out.

This also means that, when you run a pip install command, pip only
considers the packages you are installing in that command, and may
break already-installed packages. It will not guarantee that your
environment will be consistent all the time. If you pip install x
and then pip install y, it’s possible that the version of y
you get will be different than it would be if you had run pip
install x y in a single command. We are considering changing this
behavior (per :issue:`7744`) and would like your thoughts on what
pip’s behavior should be; please answer our survey on upgrades that
create conflicts.

We are also changing our support for :ref:`Constraints Files`,
editable installs, and related functionality. We did a fairly
comprehensive overhaul and stripped constraints files down to being
purely a way to specify global (version) limits for packages, and so
some combinations that used to be allowed will now cause
errors. Specifically:

• Constraints don’t override the existing requirements; they simply
  constrain what versions are visible as input to the resolver (see
  :issue:`9020`)
• Providing an editable requirement (-e .) does not cause pip to
  ignore version specifiers or constraints (see :issue:`8076`), and if
  you have a conflict between a pinned requirement and a local
  directory then pip will indicate that it cannot find a version
  satisfying both (see :issue:`8307`)
• Hash-checking mode requires that all requirements are specified as a
  == match on a version and may not work well in combination with
  constraints (see :issue:`9020` and :issue:`8792`)
• If necessary to satisfy constraints, pip will happily reinstall
  packages, upgrading or downgrading, without needing any additional
  command-line options (see :issue:`8115` and :doc:`development/architecture/upgrade-options`)
• Unnamed requirements are not allowed as constraints (see :issue:`6628` and :issue:`8210`)
• Links are not allowed as constraints (see :issue:`8253`)
• Constraints cannot have extras (see :issue:`6628`)

Per our :ref:`Python 2 Support` policy, pip 20.3 users who are using
Python 2 will use the legacy resolver by default. Python 2 users
should upgrade to Python 3 as soon as possible, since in pip 21.0 in
January 2021, pip dropped support for Python 2 altogether.

How to upgrade and migrate

1. Install pip 20.3 with python -m pip install --upgrade pip.

2. Validate your current environment by running pip check. This
   will report if you have any inconsistencies in your set of installed
   packages. Having a clean installation will make it much less likely
   that you will hit issues with the new resolver (and may
   address hidden problems in your current environment!). If you run
   pip check and run into stuff you can’t figure out, please ask
   for help in our issue tracker or chat.

3. Test the new version of pip.

   While we have tried to make sure that pip’s test suite covers as
   many cases as we can, we are very aware that there are people using
   pip with many different workflows and build processes, and we will
   not be able to cover all of those without your help.

   • If you use pip to install your software, try out the new resolver
     and let us know if it works for you with pip install. Try:
     • installing several packages simultaneously
     • re-creating an environment using a requirements.txt file
     • using pip install --force-reinstall to check whether
       it does what you think it should
     • using constraints files
     • the «Setups to test with special attention» and «Examples to try» below
   • If you have a build pipeline that depends on pip installing your
     dependencies for you, check that the new resolver does what you
     need.
   • Run your project’s CI (test suite, build process, etc.) using the
     new resolver, and let us know of any issues.
   • If you have encountered resolver issues with pip in the past,
     check whether the new resolver fixes them, and read :ref:`Fixing
     conflicting dependencies`. Also, let us know if the new resolver
     has issues with any workarounds you put in to address the
     current resolver’s limitations. We’ll need to ensure that people
     can transition off such workarounds smoothly.
   • If you develop or support a tool that wraps pip or uses it to
     deliver part of your functionality, please test your integration
     with pip 20.3.

4. Troubleshoot and try these workarounds if necessary.

   • If pip is taking longer to install packages, read :doc:`Dependency
     resolution backtracking <topics/dependency-resolution>` for ways to
     reduce the time pip spends backtracking due to dependency conflicts.
   • If you don’t want pip to actually resolve dependencies, use the
     --no-deps option. This is useful when you have a set of package
     versions that work together in reality, even though their metadata says
     that they conflict. For guidance on a long-term fix, read
     :ref:`Fixing conflicting dependencies`.
   • If you run into resolution errors and need a workaround while you’re
     fixing their root causes, you can choose the old resolver behavior using
     the flag --use-deprecated=legacy-resolver. This will work until we
     release pip 21.0 (see
     :ref:`Deprecation timeline for 2020 resolver changes`).

5. Please report bugs through the resolver testing survey.

Setups to test with special attention

• Requirements files with 100+ packages
• Installation workflows that involve multiple requirements files
• Requirements files that include hashes (:ref:`hash-checking mode`)
  or pinned dependencies (perhaps as output from pip-compile within
  pip-tools)
• Using :ref:`Constraints Files`
• Continuous integration/continuous deployment setups
• Installing from any kind of version control systems (i.e., Git, Subversion, Mercurial, or CVS), per :doc:`topics/vcs-support`
• Installing from source code held in local directories

Examples to try

Install:

• tensorflow
• hacking
• pycodestyle
• pandas
• tablib
• elasticsearch and requests together
• six and cherrypy together
• pip install flake8-import-order==0.17.1 flake8==3.5.0 --use-feature=2020-resolver
• pip install tornado==5.0 sprockets.http==1.5.0 --use-feature=2020-resolver

Try:

• pip install
• pip uninstall
• pip check
• pip cache

Tell us about

Specific things we’d love to get feedback on:

• Cases where the new resolver produces the wrong result,
  obviously. We hope there won’t be too many of these, but we’d like
  to trap such bugs before we remove the legacy resolver.
• Cases where the resolver produced an error when you believe it
  should have been able to work out what to do.
• Cases where the resolver gives an error because there’s a problem
  with your requirements, but you need better information to work out
  what’s wrong.
• If you have workarounds to address issues with the current resolver,
  does the new resolver let you remove those workarounds? Tell us!

Please let us know through the resolver testing survey.

Deprecation timeline

We plan for the resolver changeover to proceed as follows, using
:ref:`Feature Flags` and following our :ref:`Release Cadence`:

• pip 20.1: an alpha version of the new resolver was available,
  opt-in, using the optional flag
  --unstable-feature=resolver. pip defaulted to legacy
  behavior.
• pip 20.2: a beta of the new resolver was available, opt-in, using
  the flag --use-feature=2020-resolver. pip defaulted to legacy
  behavior. Users of pip 20.2 who want pip to default to using the
  new resolver can run pip config set global.use-feature
2020-resolver (for more on that and the alternate
  PIP_USE_FEATURE environment variable option, see issue
  8661).
• pip 20.3: pip defaults to the new resolver in Python 3 environments,
  but a user can opt-out and choose the old resolver behavior,
  using the flag --use-deprecated=legacy-resolver. In Python 2
  environments, pip defaults to the old resolver, and the new one is
  available using the flag --use-feature=2020-resolver.
• pip 21.0: pip uses new resolver by default, and the old resolver is
  no longer supported. It will be removed after a currently undecided
  amount of time, as the removal is dependent on pip’s volunteer
  maintainers’ availability. Python 2 support is removed per our
  :ref:`Python 2 Support` policy.

Since this work will not change user-visible behavior described in the
pip documentation, this change is not covered by the :ref:`Deprecation
Policy`.

Context and followup

As discussed in our announcement on the PSF blog, the pip team are
in the process of developing a new «dependency resolver» (the part of
pip that works out what to install based on your requirements).

We’re tracking our rollout in :issue:`6536` and you can watch for
announcements on the low-traffic packaging announcements list and
the official Python blog.

Using system trust stores for verifying HTTPS

This is now covered in :doc:`topics/https-certificates`.