If you should ever encounter the following error when creating a Python virtual environment using the pyvenv command:
user$ pyvenv my_venv_dir
Error: Command '['/home/user/my_venv_dir/bin/python', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1
... then the answer (below) provides a simple way to work around it, without resorting to setuptools and it's related acrobatics.
Here's an approach that is fairly O/S agnostic...
Both the pyvenv and python commands themselves include a --without-pip option that enable you to work around this issue; without resorting to setuptool or other headaches. Taking note of my inline comments below, here's how to do it, and is very easy to understand:
user$ pyvenv --without-pip ./pyvenv.d # Create virtual environment this way;
user$ python -m venv --without-pip ./pyvenv.d # --OR-- this newer way. Both work.
user$ source ./pyvenv.d/bin/activate # Now activate this new virtual environment.
(pyvenv.d) user$
# Within it, invoke this well-known script to manually install pip(1) into /pyvenv.d:
(pyvenv.d) user$ curl https://bootstrap.pypa.io/get-pip.py | python
(pyvenv.d) user$ deactivate # Next, reactivate this virtual environment,
user$ source ./pyvenv.d/bin/activate # which will now include the pip(1) command.
(pyvenv.d) user$
(pyvenv.d) user$ which pip # Verify that pip(1) is indeed present.
/path/to/pyvenv.d/bin/pip
(pyvenv.d) user$ pip install --upgrade pip # And finally, upgrade pip(1) itself;
(pyvenv.d) user$ # although it will likely be the
# latest version already.
# And that's it!
I hope this helps. \(◠﹏◠)/