def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, 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)