def lt_pre_release(self, other):
    """
    Check to see if one SemVer's pre_release version is less than that of
    another. From the SemVer spec:

        Pre-release versions have a lower precedence than the associated
        normal version.

    """
    if self.pre_release and other.pre_release:
        return self.pre_release < other.pre_release
    elif self.pre_release and not other.pre_release:
        return True
    return False