Sympy definite integral

I want to integrate the equation:

f(x) = integral(E^(-i * omega * t)), from -a to a.

I wrote the following code:

from sympy import *
from sympy.abc import a, omega, t

init_printing(use_unicode=False, wrap_line=False, no_global=True)


f = E**(-I * omega * t)    

integrate(f, (omega, -a, a))

But the result is just the entered definite integral. When I change the integrally limits to 0 to a I get a result... Does anyone know how to get a solution from -a to a?

Many thanks in advance.

John