How to obtain arguments passed to setup.py from pip with ‘–install-option’?

You need to extend the install command with a custom command of your own. In the run method you can expose the value of the option to setup.py (in my example I use a global variable).

from setuptools.command.install import install


class InstallCommand(install):
    user_options = install.user_options + [
        ('someopt', None, None), # a 'flag' option
        #('someval=", None, None) # an option that takes a value
    ]

    def initialize_options(self):
        install.initialize_options(self)
        self.someopt = None
        #self.someval = None

    def finalize_options(self):
        #print("value of someopt is", self.someopt)
        install.finalize_options(self)

    def run(self):
        global someopt
        someopt = self.someopt # will be 1 or None
        install.run(self)

Register the custom install command with the setup function.

setup(
    cmdclass={
        "install': InstallCommand,
    },
    :

It seems that the order of your arguments is off

pip install /path/to/my/local/package --install-option="--someopt"