see https://pip.pypa.io/en/stable/reference/pip_install/#controlling-setup-requires > Setuptools offers the setup_requires setup() keyword for specifying > dependencies that need to be present in order for the setup.py > script to run. Internally, Setuptools uses easy_install to > fulfill these dependencies. > pip has no way to control how these dependencies are located. > None of the package index options have an effect. With these changes, we will now instead hard fail if this were to happen. related: https://github.com/spesmilo/electrum/issues/5859#issuecomment-743621898