When users install the pipx pkg, there is an expectation that apt will
automatically install all necessary dependencies. Here is a sample
command after installing pipx:

===✂----------------------------------------
$ pipx install --pip-args='--find-links wheel_cache' .
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f882e8ffc10>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/pip/
WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f882e908890>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/pip/
WARNING: Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f882e908f50>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/pip/
WARNING: Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f882e909cd0>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/pip/
WARNING: Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f882e90a3d0>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/pip/
ERROR: Could not find a version that satisfies the requirement pip (from versions: none)
ERROR: No matching distribution found for pip
Failed to upgrade shared libraries
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/pipx/shared_libs.py", line 113, in upgrade
    subprocess_post_check(upgrade_process)
  File "/usr/lib/python3/dist-packages/pipx/util.py", line 203, in subprocess_post_check
    raise PipxError(
pipx.util.PipxError: '/root/.local/pipx/shared/bin/python -m pip --disable-pip-version-check install --force-reinstall -q --upgrade pip setuptools wheel'
failed
===✂----------------------------------------

About the warnings: they are an unrelated problem. All needed wheels
were put in a directory called “wheel_cache” and the installation was
launched from an offline machine. Attempts were still made to reach
the cloud.

The errors are what is relevant to this bug report herein. There was
no “pip” command available because python3-pip was not explicitly
installed. Nor was it implicitly installed when running “aptitude
install pipx”.