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* 581: Instead of vendoring the growing list of
dependencies that Setuptools requires to function,
Setuptools now requires these dependencies just like
any other project. Unlike other projects, however,
Setuptools cannot rely on ``setup_requires`` to
demand the dependencies it needs to install because
its own machinery would be necessary to pull those
dependencies if not present (a bootstrapping problem).
As a result, Setuptools no longer supports self upgrade or
installation in the general case. Instead, users are
directed to use pip to install and upgrade using the
``wheel`` distributions of setuptools.
Users are welcome to contrive other means to install
or upgrade Setuptools using other means, such as
pre-installing the Setuptools dependencies with pip
or a bespoke bootstrap tool, but such usage is not
recommended and is not supported.
As discovered in 940, not all versions of pip will
successfully install Setuptools from its pre-built
wheel. If you encounter issues with "No module named
six" or "No module named packaging", especially
following a line "Running setup.py egg_info for package
setuptools", then your pip is not new enough.
There's an additional issue in pip where setuptools
is upgraded concurrently with other source packages,
described in pip 4253. The proposed workaround is to
always upgrade Setuptools first prior to upgrading
other packages that would upgrade Setuptools.