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 __init__(self, p1, p2):
        self.p1 = p1
        self.p2 = p2
        # 直線的第一點, 設為線尾
        self.Tail = self.p1
        # 直線組成的第二點, 設為線頭
        self.Head = self.p2
        # 直線的長度屬性
        self.length = math.sqrt(math.pow(self.p2.x-self.p1.x, 2)+math.pow(self.p2.y-self.p1.y,2))