Updating pip with Python 2.7.5 breaks pip

Description

When updating to pip 21.1.2 for Python 2.7.5, pip is broken (usage of f-string for formatting strings, giving a “invalid syntax” message).

Expected behavior

As I understand, Python 2 is not supported by pip anymore, but pip should neither :

• suggest to upgrade to 21.1.2 when running with Python 2;
• actually upgrade to a script with invalid syntax

pip version

21.1.2

Python version

2.7.5

OS

CentOS Linux release 7.9.2009 (Core)

How to Reproduce

1. When pip has been upgraded to version 21.1.2 it fails
2. We can workaround this by uninstalling pip and resinstalling old version from yum package:
3. Then upgrading pip with itself to a known-to-work version (here version 20.0.2), but pip still insists that we should update to version 21.1.2.

Output

1. When pip has been upgraded to version 21.1.2 it fails like this:

$ python -m pip --version
Traceback (most recent call last):
  File "/usr/lib64/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib64/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/usr/lib/python2.7/site-packages/pip/__main__.py", line 29, in <module>
    from pip._internal.cli.main import main as _main
  File "/usr/lib/python2.7/site-packages/pip/_internal/cli/main.py", line 58
    sys.stderr.write(f"ERROR: {exc}")
                                   ^
SyntaxError: invalid syntax

1. We can workaround this by uninstalling pip and resinstalling old version from yum package:

$ sudo yum remove python-pip
[sudo] password for admin:
Loaded plugins: fastestmirror
Resolving Dependencies
--> Running transaction check
---> Package python2-pip.noarch 0:8.1.2-14.el7 will be erased
--> Finished Dependency Resolution

Dependencies Resolved

==================================================================================================================================================================
 Package                                  Arch                                Version                                    Repository                          Size
==================================================================================================================================================================
Removing:
 python2-pip                              noarch                              8.1.2-14.el7                               @epel                              7.2 M

Transaction Summary
==================================================================================================================================================================
Remove  1 Package

Installed size: 7.2 M
Is this ok [y/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Erasing    : python2-pip-8.1.2-14.el7.noarch                                                                                                                1/1
warning: file /usr/lib/python2.7/site-packages/pip/wheel.pyo: remove failed: No such file or directory
 [...]
warning: file /usr/lib/python2.7/site-packages/pip-8.1.2-py2.7.egg-info: remove failed: No such file or directory
warning: file /usr/bin/pip: remove failed: No such file or directory
  Verifying  : python2-pip-8.1.2-14.el7.noarch                                                                                                                1/1

Removed:
  python2-pip.noarch 0:8.1.2-14.el7

Complete!


$ sudo rm -fr /usr/lib/python2.7/site-packages/pip
[sudo] password for admin:
$ sudo rm -fr /usr/lib/python2.7/site-packages/pip-2*

$ sudo yum install python-pip
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
epel/x86_64/metalink                                                                                                                       |  13 kB  00:00:00
 * base: centos.crazyfrogs.org
 * epel: d2lzkl7pfhq30w.cloudfront.net
 * extras: centos.crazyfrogs.org
 * updates: centos.crazyfrogs.org
base                                                                                                                                       | 3.6 kB  00:00:00
docker-ce-stable                                                                                                                           | 3.5 kB  00:00:00
epel                                                                                                                                       | 4.7 kB  00:00:00
extras                                                                                                                                     | 2.9 kB  00:00:00
updates                                                                                                                                    | 2.9 kB  00:00:00
(1/2): epel/x86_64/updateinfo                                                                                                              | 1.0 MB  00:00:00
(2/2): epel/x86_64/primary_db                                                                                                              | 6.9 MB  00:00:00
Resolving Dependencies
--> Running transaction check
---> Package python2-pip.noarch 0:8.1.2-14.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

==================================================================================================================================================================
 Package                                  Arch                                Version                                     Repository                         Size
==================================================================================================================================================================
Installing:
 python2-pip                              noarch                              8.1.2-14.el7                                epel                              1.7 M

Transaction Summary
==================================================================================================================================================================
Install  1 Package

Total download size: 1.7 M
Installed size: 7.2 M
Is this ok [y/d/N]: y
Downloading packages:
python2-pip-8.1.2-14.el7.noarch.rpm                                                                                                        | 1.7 MB  00:00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : python2-pip-8.1.2-14.el7.noarch                                                                                                                1/1
  Verifying  : python2-pip-8.1.2-14.el7.noarch                                                                                                                1/1

Installed:
  python2-pip.noarch 0:8.1.2-14.el7

Complete!

1. then upgrading pip with itself to a known-to-work version (here version 20.0.2)

$ sudo pip2 install --upgrade pip==20.0.2
Collecting pip==20.0.2
  Cache entry deserialization failed, entry ignored
  Using cached https://files.pythonhosted.org/packages/54/0c/d01aa759fdc501a58f431eb594a17495f15b88da142ce14b5845662c13f3/pip-20.0.2-py2.py3-none-any.whl
Installing collected packages: pip
  Found existing installation: pip 8.1.2
    Uninstalling pip-8.1.2:
      Successfully uninstalled pip-8.1.2
Successfully installed pip-20.0.2
You are using pip version 20.0.2, however version 21.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
WARNING: You are using pip version 20.0.2; however, version 21.1.2 is available.
You should consider upgrading via the '/usr/bin/python2 -m pip install --upgrade pip' command.

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[SESA123456]

@uranusjr you’re right!

When listing installed packages (for example), the warning is different (version 20.3.4 is suggested for upgrading instead of 21.1.2):

$ pip2 list
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. A future version of pip will drop support for Python 2.7. More details about Python 2 support in pip, can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
Package                          Version
-------------------------------- ----------
asn1crypto                       0.24.0
  [...]
yum-metadata-parser              1.1.4
WARNING: You are using pip version 20.0.2; however, version 20.3.4 is available.
You should consider upgrading via the '/usr/bin/python2 -m pip install --upgrade pip' command.

And when actually upgrading (without version constraint), pip goes up to version 20.3.4 and not 21.1.2:

$ sudo pip2 install --upgrade pip
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. A future version of pip will drop support for Python 2.7. More details about Python 2 support in pip, can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
Collecting pip
  Using cached pip-20.3.4-py2.py3-none-any.whl (1.5 MB)
Installing collected packages: pip
  Attempting uninstall: pip
    Found existing installation: pip 20.0.2
    Uninstalling pip-20.0.2:
      Successfully uninstalled pip-20.0.2
Successfully installed pip-20.3.4

No more incentives for upgrading are issued afterwards.

Thanks for all these clarifications.

Have a nice day.

[uranusjr]

Actually, a reasonably up-to-date pip will not warn about incompatible pip versions (and will also stop you from doing that). But the built-in pip in Python 2.7 is from like five years ago and doesn’t have that functionality. This applies not only to pip but almost every projects that is still being worked on, everyone is slowly dropping Python 2 support. If you somehow still must run Python 2, you probably shouldn’t upgrade anything unless you really really know what the new version is changing.