TypeError: object is not callable when solving for 1st order ODEs?

Question

This is the code I've written and been provided with, and below is the error I am repeatedly getting. I've tried using both y.diff & Derivative functions in this code, but both of them give me the same error.

#y'-2ty = -t
from sympy import *

t = symbols('t')
y = Function('y')(t)

eqn = (Derivative(y(t)) - (2*t*y(t)), -t)
display(eqn)

ysol = dsolve(eqn,y(t))
print("The solution is ", ysol.lhs, " = ", ysol.rhs)
print("The solution is ") 
display(ysol)

Error:

----> 1 ysol = dsolve(eqn,y(t))

TypeError: 'y' object is not callable

Answer 1

The line

y = Function('y')(t)

already defines y as a function of t. When you write y(t) later, you're asking sympy to call y as if it's a function (like when you call the print function as print(...)). You have two options: (1) Don't define y as a function of t, i.e.

y = Function('y')

With that change, you will no longer get the error. (2) Keep y defined as it is but later only write y instead of y(t), i.e.

eqn = (Derivative(y) - (2*t*y), -t)

In your question you said you tried y.diff(), but with how you've defined y, that should actually work, so I'm guess you actually did y(t).diff().

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Now, you actually have another issue later, which is that you should define eqn as a sympy equation, i.e.

eqn = Eq(Derivative(y) - (2*t*y), -t)

Without that, dsolve will throw an error (it's expecting an equation).

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As another minor point, avoid wildcard imports (from X import *) in your code. Some people will do import sympy as smp or import sympy as sp or just import sympy. Then, you would do y = smp.Function("y").