>>> x, y, t = sympy.symbols('x, y, t')
>>> from sympy import Derivative
>>> f2 = 2003 - 6002/y + 4000/(x*y)
>>> d1 = Derivative(f2,x).doit() 
>>> d2 = Derivative(f2,y).doit() ; d1, d2
(-4000/(x**2*y), 6002/y**2 - 4000/(x*y**2))