def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def setSAS(self, lenp3, ap2, lenp1):
        self.lenp3 = lenp3
        self.ap2 = ap2
        self.lenp1 = lenp1
        self.lenp2 = math.sqrt((self.lenp3 * self.lenp3 + self.lenp1 * self.lenp1) - 2* self.lenp3 * self.lenp1 * math.cos(self.ap2))
        #等於 SSS(AB, BC, CA)