'Called before python modules\' install() methods.
In most cases, extensions will only need to have one line::
setup_py(\'install\', \'--prefix={0}\'.format(prefix))'

def setup_dependent_package(self, module, dependent_spec):

    module.python = self.command
    module.setup_py = Executable((self.command.path + '    setup.py    --no-user-cfg'))
    distutil_vars = self._load_distutil_vars()
    if distutil_vars:
        for (key, value) in distutil_vars.items():
            module.setup_py.add_default_env(key, value)
    module.python_lib_dir = join_path(dependent_spec.prefix, self.python_lib_dir)
    module.python_include_dir = join_path(dependent_spec.prefix, self.python_include_dir)
    module.site_packages_dir = join_path(dependent_spec.prefix, self.site_packages_dir)
    self.spec.home = self.home
    if dependent_spec.package.is_extension:
        mkdirp(module.site_packages_dir)
