'Install everything in this set (after having downloaded and unpacked the packages)'

def install(self, install_options, global_options=()):

    to_install = [r for r in self.requirements.values() if (self.upgrade or (not r.satisfied_by))]
    if to_install:
        logger.notify(('Installing    collected    packages:    %s' % ',    '.join([req.name for req in to_install])))
    logger.indent += 2
    try:
        for requirement in to_install:
            if requirement.conflicts_with:
                logger.notify(('Found    existing    installation:    %s' % requirement.conflicts_with))
                logger.indent += 2
                try:
                    requirement.uninstall(auto_confirm=True)
                finally:
                    logger.indent -= 2
            try:
                requirement.install(install_options, global_options)
            except:
                if (requirement.conflicts_with and (not requirement.install_succeeded)):
                    requirement.rollback_uninstall()
                raise
            else:
                if (requirement.conflicts_with and requirement.install_succeeded):
                    requirement.commit_uninstall()
            requirement.remove_temporary_source()
    finally:
        logger.indent -= 2
    self.successfully_installed = to_install
