ResolvePackageNotFound - dateutil even after installing dateutil

[particlekitty]

Hello, I am on xUbuntu 18.04 with a fresh conda env with base python 3. I installed dateutil via
pip install python-dateutil
but I could also do
conda install python-dateutil

but when I attempt to follow the ddt installation instructions for local development via:
https://domain-discovery-tool.readthedocs.io/en/latest/install.html

I get the following print out and error when I get to the "make" step:
$> make
conda env update
Collecting package metadata (repodata.json): done
Solving environment: failed

ResolvePackageNotFound:

• dateutil

Makefile:42: recipe for target '/home/ache/anaconda3/envs/dd_api/conda-meta/history' failed
make: *** [/home/ache/anaconda3/envs/dd_api/conda-meta/history] Error 1

I have attempted this with two different conda envs, one with python 3 and the other with python 2.7.
In either case, when I do
conda list
after the installation of python-dateutil, I can see it, but of course it isn't named "dateutil" -- it's named python-dateutil. I could not install it with conda/pip install dateutil.

Any help you can provide to get this local copy working would be great. Otherwise, I'll try to use the ddt with docker.
Thanks!