Python2 pip cannot update to pip-21.0.1 sys.stderr.write(f“ERROR: {exc}”)

[Yanos Angelopoulos]

Trying to build an image I have faced the following issue:

 Setting up python-pip (9.0.1-2.3~ubuntu1.18.04.4) ...
 Collecting pip
   Downloading pip-21.0.1-py3-none-any.whl (1.5 MB)
 Collecting setuptools
   Downloading setuptools-53.0.0-py3-none-any.whl (784 kB)
 Collecting wheel
   Downloading wheel-0.36.2-py2.py3-none-any.whl (35 kB)
 Installing collected packages: wheel, setuptools, pip
   Attempting uninstall: pip
     Found existing installation: pip 9.0.1
     Uninstalling pip-9.0.1:
       Successfully uninstalled pip-9.0.1
 Successfully installed pip-21.0.1 setuptools-53.0.0 wheel-0.36.2
 Traceback (most recent call last):
   File "/tmp/get-pip.py", line 24244, in <module>
     main()
   File "/tmp/get-pip.py", line 199, in main
     bootstrap(tmpdir=tmpdir)
   File "/tmp/get-pip.py", line 82, in bootstrap
     from pip._internal.cli.main import main as pip_entry_point
   File "/tmp/tmp6hqCIU/pip.zip/pip/_internal/cli/main.py", line 60
     sys.stderr.write(f"ERROR: {exc}")

Caused by: https://opendev.org/openstack/diskimage-builder/src/branch/master/diskimage_builder/elements/pip-and-virtualenv/install.d/pip-and-virtualenv-source-install/04-install-pip#L257

Python2 pip is trying to update to pip-21.0.1 and fails.