How can I remove higher order term using SymPy? .removeO() does not work here

I am trying to plot the series form of an ODE's solution using SymPy, and I need to remove the 'O' term before plotting.

from IPython.display import display
from sympy import *
from sympy.plotting import plot

x = Function('x')
t = Symbol('t')
ode = Derivative(x(t),t) + t * x(t) - t**3

sol_series = dsolve(ode, hint='1st_power_series', n=8, ics={x(0): 1})
res = sol_series.removeO()

But here comes error

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-66-2775b6fd4150> in <module>
----> 1 res = sol_series.removeO()
      2 display(res)

AttributeError: 'Equality' object has no attribute 'removeO'

How to solve this problem?

Solution

That's because the return from dsolve is an Eq (equation object) and the removeO method is for Expr so you should call removeO in the rhs of the equation:

In [5]: res = Eq(sol_series.lhs, sol_series.rhs.removeO())                                                                                                    

In [6]: res                                                                                                                                                   
Out[6]: 
          6      4    2    
         t    3⋅t    t     
x(t) = - ── + ──── - ── + 1
         16    8     2