"这是我的错误"

Traceback (most recent call last):

  File "C:\Users\user\.spyder-py3\Numerical Methods Problems\FreeFall.py", line 40, in <module>
    ans=odeint(vel,0,t)

  File "C:\ProgramData\Anaconda3\lib\site-packages\scipy\integrate\odepack.py", line 245, in odeint
    int(bool(tfirst)))

  File "C:\ProgramData\Anaconda3\lib\site-packages\sympy\core\expr.py", line 325, in __float__
    raise TypeError("can't convert expression to float")

TypeError: can't convert expression to float

这是我的代码--我对编码还很陌生，正在学习用它来进行数值计算：

from scipy.integrate import odeint
from sympy import *
import numpy as np
import math

def diff_cd(re_no):
    Re=Symbol('Re')
    expr=(24/Re)+(6/(1+(Re**0.5)))+0.4
    ans=diff(expr,Re).subs(Re,re_no)    
    return ans

def diff_re(k,u_no):
    u=Symbol('u')
    expr=k*u
    ans=diff(expr,u).subs(u,u_no)
    return ans    

ans = [diff_cd(20),diff_re(11,15)]

rhog=1.2
mug=1.872*(10**(-5))
a=0.3

u=Symbol('u')
pi=math.pi

k=(2*rhog*a/mug)
Re=k*u

p1=(rhog*pi*(a**2)*u*Re*((24/Re)+(6/(1+(Re**0.5)))+0.4))+(0.5*rhog*pi*(a**2)*(u**2)*diff_cd(Re)*diff_re(k,u))

ansfu=p1*(-1/24)

def vel(y,t):
    dudt = ansfu
    return dudt

t=np.linspace(1,100,100)
ans=odeint(vel,0,t)

print(ans)

我只需要得到一个没有这个错误的答案。还有有没有办法在一个单一的函数中完成所有这些