Update class instance

I'm a beginner in Python and have a trouble in running a python module in Rhino3D Grasshopper. The code in a Python module is shown as below. An instance of Agent alone is working well but when I try to dla.update() with Timer in a next python module(which is simply executing dla.update()), I got the message saying that there is something wrong in self.pos = rs.EvaluateCurve(cirCrv, rndNum) and self.curAgent = Agent(self.cirCrv, self.cenPt, self.walkDist).

Is there a way to make this working ?

import rhinoscriptsyntax as rs
import Rhino.Geometry as rg
import ghpythonlib.components as gh
import random as rnd


class Agent :
    def __init__(self, cirCrv, cenPt, walkDist):
        self.cenPt = cenPt
        self.walkDist = walkDist
        rndNum = rnd.random()
        self.pos = rs.EvaluateCurve(cirCrv, rndNum)

    def randWalk(self) :
        v = rs.VectorSubtract(rs.AddPoint(0,0,0), self.pos)
        v1 = rs.VectorUnitize(v)
        v2 = rs.VectorScale(v1, self.walkDist)
        v3 = rs.VectorSubtract(self.pos, rs.AddPoint(0,0,0))
        v4 = rs.VectorAdd(v3, gh.UnitZ(1))
        rotAxis = rs.VectorSubtract(v4, v3)
        newV1 = rs.VectorRotate(v2, rnd.uniform(-70, 70), rotAxis)
        self.pos = rs.VectorAdd(self.pos, newV1)

    def checkDist(self):

        dist1 = rs.Distance(self.pos, rs.AddPoint(0,0,0))
        return dist1


class dla :

    def __init__(self, cirCrv, cenPt, walkDist):
        self.Agents = []
        self.cirCrv = cirCrv
        self.cenPt = cenPt
        self.walkDist = walkDist
        self.curAgent = Agent(self.cirCrv, self.cenPt, self.walkDist)
        self.pos =self.curAgent.pos 


    def update(self):
        if self.curAgent.checkDist() < 1:
           self.Agents.append(self.curAgent)
           self.curAgent = Agent(self.cirCrv, self.cenPt, self.walkDist)
        else:
            self.curAgent.randWalk()

a = dla(cirCrv,cenPt,walkDist)

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