"The 'distribute' distribution was not found and is required by stevedore"

I just upgrdade OS X to 10.15.4. I now get a series of errors everytime I launch a new terminal window:

```
stevedore.extension Could not load 'user_scripts': The 'distribute' distribution was not found and is required by stevedore
stevedore.extension The 'distribute' distribution was not found and is required by stevedore
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/stevedore/extension.py", line 75, in _load_plugins
    invoke_kwds,
  File "/usr/local/lib/python2.7/site-packages/stevedore/extension.py", line 87, in _load_one_plugin
    plugin = ep.load()
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2433, in load
    self.require(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2456, in require
    items = working_set.resolve(reqs, env, installer, extras=self.extras)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 786, in resolve
    raise DistributionNotFound(req, requirers)
DistributionNotFound: The 'distribute' distribution was not found and is required by stevedore
stevedore.extension Could not load 'project': The 'distribute' distribution was not found and is required by stevedore
```

I get similar stacktraces for stevedor failing to load `project` twice more, and `user_scripts` twice more.

I've tried a number of cycles of upgrading pip2.7, using pip2.7 to upgrade stevedore, and using pip2.7 to upgrade distribute.

Interestingly, pip2.7 thinks that it's installed/upgraded distribute:

```
Requirement already up-to-date: distribute in /Library/Python/2.7/site-packages (0.7.3)
```

However, if I do

```
$ python2.7
Python 2.7.16 (default, Sep 2 2019, 11:59:44)
[GCC 4.2.1 Compatible Apple LLVM 10.0.1 (clang-1001.0.46.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import distribute
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named distribute
```

Note: I do not use python2, personally, I'm only trying to resolve a couple of pages full of errors that get emitted every time I launch a new terminal session.

Actually, I just realized that I get all these errors every time I activate a new python3 virtualenv : (