pip 20.3 release (heads-up for potential disruption)

[Sumana Harihareswara]

On behalf of the Python Packaging Authority, I am pleased to announce 
that we have just released pip 20.3, a new version of pip. You can 
install it by running `python -m pip install --upgrade pip`.

This is an important and disruptive release -- we explained why in a
blog post last year 
https://pyfound.blogspot.com/2019/12/moss-czi-support-pip.html . We even 
made a video about it: https://www.youtube.com/watch?v=B4GQCBBsuNU .

Blog post with details: 
https://pyfound.blogspot.com/2020/11/pip-20-3-new-resolver.html

Highlights include:

* **DISRUPTION**: Switch to the new dependency resolver by
     default. Watch out for changes in handling editable
     installs, constraints files, and more:

https://pip.pypa.io/en/latest/user_guide/#changes-to-the-pip-dependency-resolver-in-20-3-2020

* **DEPRECATION**: Deprecate support for Python 3.5 (to be removed in
     pip 21.0)

* **DEPRECATION**: pip freeze will stop filtering the pip, setuptools,
     distribute and wheel packages from pip freeze output in a future
     version. To keep the previous behavior, users should use the new
     `--exclude` option.

* Support for PEP 600: Future ‘manylinux’ Platform Tags for Portable
   Linux Built Distributions.

* Add support for MacOS Big Sur compatibility tags.

The new resolver is now *on by default*. It is significantly stricter
and more consistent when it receives incompatible instructions, and
reduces support for certain kinds of constraints files, so some
workarounds and workflows may break. Please see our guide on how to
test and migrate, and how to report issues: 
https://pip.pypa.io/en/latest/user_guide/#changes-to-the-pip-dependency-resolver-in-20-3-2020 
. You can use the deprecated (old) resolver, using the flag
`--use-deprecated=legacy-resolver`, until we remove it in the pip 21.0
release in January 2021.

In pip 21.0 we will also remove support for Python 2.7.

You can find more details (including deprecations and removals) in the
changelog https://pip.pypa.io/en/stable/news/ , and you can find 
thank-yous and instructions on reporting issues at 
https://pyfound.blogspot.com/2020/11/pip-20-3-new-resolver.html .

Thank you,
Sumana Harihareswara
pip project manager
Changeset Consulting
https://changeset.nyc