getting a few python packages onto the jetson-nano (or most anything with
a Debian-style linux, for example a raspberry pi)
without an internet connection.

Assuming another Debian or Debian-derived linux box (ubuntu or raspbian)
that does have an internet connection.

===== On the machine with an internet connection =====

First, download the python-pip packages.  for both python 2 and python 3:
  apt-get download python-pip python3-pip
two files should be downloaded (check with ls):
  python-pip_9.0.1-2.3~ubuntu1.18.04.1_all.deb
  python3-pip_9.0.1-2.3~ubuntu1.18.04.1_all.deb

These are native ubuntu '.deb' packages.
Copy them to the usb stick.

Next, download the python packages we need, using pip:
  pip download imutils
  pip download pynetworktables

pynetworktables depends on another package called monotonic, so there should be 3 more files:
  imutils-0.5.3.tar.gz
  monotonic-1.5-py2.py3-none-any.whl
  pynetworktables-2018.2.1-py2.py3-none-any.whl

copy them to the usb stick too.

----

===== On the Nano without Internet =====

move the usb stick to the nano; copy all of those files above to a
folder called for example download/cv-tools

First, we have to install pip:

  sudo dpkg -i download/cv-tools/python-pip_9.0.1-2.3~ubuntu1.18.04.1_all.deb
  sudo dpkg -i download/cv-tools/python3-pip_9.0.1-2.3~ubuntu1.18.04.1_all.deb

Next, install those python packages, using the pip command htat we
just installed, but running these commands:

  cd download
  pip install imutils --no-index --find-links cv-tools/
  pip install pynetworktables --no-index --find-links cv-tools/

The options "--no-index --find-links cv-tools/" tell pip not to use
the internet for the package index and to download stuff, but to use
only what's in the cv-tools directory.

After that, I can run our python opencv script without crashing due to
missing packages.