normpath.py 文件源码

def tangent_pt(self, params, length_pt):
        """return tangent vector of path at param(s) or arc length(s) in pts

        If length in pts is not None, the tangent vector will be scaled to
        the desired length.
        """
        return self._tangent(self._convertparams(params, self.arclentoparam_pt), length_pt)