def __init__(self, package, version):
        """Construct a new requirement.

        :param package: the package name.
        :param version: a semver compatible version specification.
        """
        self.package = package
        self.version = version
        if self.version and not re.match(r"[<=>~]", version[:2]):
            self.version = "=={}".format(self.version)
def run(self):
    hdrs = self.distribution.headers
    if not hdrs:
      return

    self.mkpath(self.install_dir)
    for header in hdrs:
      (out, _) = self.mkdir_and_copy_file(header)
      self.outfiles.append(out)