sympy/sympy — pull request #1803 by Manoj-Kumar-S (2013-02-19 16:56:16+00:00)
Title: Incorrect Exception in dsolve() : First implementation

This pull request is related to the issue http://code.google.com/p/sympy/issues/detail?id=1996

As mentioned in the above link , dsolve() returns wrong exceptions when it is not solvable , and the hint is either invalid or incorrect.

from sympy import *
from sympy.abc import x
f = Function('f')
dsolve(f(x).diff(x)**2, f(x), 'separable') #This now gives the correct ValueError
>>> ValueError: ODE Derivative(f(x), x)**2 does not match hint separable

Also , as mentioned in the link as needed

dsolve(f(x).diff(x)**2, f(x), 'fdsjf') #This should give ValueError for incorrect hint
>>> ValueError: Hint not recognized: fdsjf

Do look at the code for changes required.