code: def install_given_reqs(
      to_install,  # type: List[InstallRequirement]
      install_options,  # type: List[str]
      global_options=(),  # type: Sequence[str]
      *args, **kwargs
  ):
      # type: (...) -> List[InstallRequirement]
      
  
      if to_install:
          logger.info(
              'Installing collected packages: %s',
              ', '.join([req.name for req in to_install]),
          )
  
      with indent_log():
          for requirement in to_install:
              if requirement.conflicts_with:
                  logger.info(
                      'Found existing installation: %s',
                      requirement.conflicts_with,
                  )
                  with indent_log():
                      uninstalled_pathset = requirement.uninstall(
                          auto_confirm=True
                      )
              try:
                  requirement.install(
                      install_options,
                      global_options,
                      *args,
                      **kwargs
                  )
              except Exception:
                  should_rollback = (
                      requirement.conflicts_with and
                      not requirement.install_succeeded
                  )
                  # if install did not succeed, rollback previous uninstall
                  if should_rollback:
                      uninstalled_pathset.rollback()
                  raise
              else:
                  should_commit = (
                      requirement.conflicts_with and
                      requirement.install_succeeded
                  )
                  if should_commit:
                      uninstalled_pathset.commit()
              requirement.remove_temporary_source()
  
      return to_install
docs: Install everything in the given list.
  
      (to be called after having downloaded and unpacked the packages)