While installing nylas, I realized it also pulled the following:

bumpversion = ">=0.5.0"
six = ">=1.4.1"
urlobject = "*"

And indeed it's in the setup.py's install_requires:

This was surprising to me, as this dependency is usually only for cutting new releases, but not actually required at runtime. Indeed, poking around a bit the only usage I see is:

Could be worth using extras_require here, so maintainers can still install those dependencies easily:

extras_require

A dictionary mapping names of “extras” (optional features of your project) to strings or lists of strings specifying what other distributions must be installed to support those features. See the section below on Declaring Dependencies for details and examples of the format of this argument.

(See https://setuptools.readthedocs.io/en/latest/setuptools.html#new-and-changed-setup-keywords)