pip upgrade inside python 2.7 environment breaks pip

[securestep9]

pip version

19.1

Python version

2.7

OS

RHEL 7.9

Additional information

No response

Description

in pip2.7 environment (yes, I know people still use Python2 as there are 1000s of systems not yet supporting python3) running a pip install --upgrade pip install version 21.1.0 which broke itself (pip2) with error:

File "/usr/bin/pip", line 9, in
load_entry_point('pip==21.0.1', 'console_scripts', 'pip2')()
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 378, in load_entry_point
return get_distribution(dist).load_entry_point(group, name)
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2566, in load_entry_point
return ep.load()
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2260, in load
entry = import(self.module_name, globals(),globals(), ['name'])
File "/usr/lib/python2.7/site-packages/pip/_internal/cli/main.py", line 60
sys.stderr.write(f"ERROR: {exc}")
^
SyntaxError: invalid syntax

Expected behavior

pip upgrade should detect that it is running in python 2.x environment an should refuse to upgrade itself beyond v.20.x

How to Reproduce

inside python 2.7 environment run:

pip install --upgrade pip

now try to run pip - get error:

Output

pip install --upgrade pip
 File "/usr/bin/pip", line 9, in <module>
    load_entry_point('pip==21.0.1', 'console_scripts', 'pip2')()
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 378, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2566, in load_entry_point
    return ep.load()
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2260, in load
    entry = __import__(self.module_name, globals(),globals(), ['__name__'])
  File "/usr/lib/python2.7/site-packages/pip/_internal/cli/main.py", line 60
    sys.stderr.write(f"ERROR: {exc}")
                                   ^
SyntaxError: invalid syntax

Code of Conduct

• I agree to follow the PSF Code of Conduct

[pfmoore]

I suspect (you don't mention the version you're upgrading from) that the version of pip you're installing from doesn't support the Requires-Python metadata that addresses this issue. So you'll have to explicitly restrict the version you're upgrading to.

The good news is that once you've upgraded, the new pip will be able to detect that newer versions don't support Python 2.7, and so will not fail in this way in future...

[uranusjr]

See discussion in #9526.