'Allow derivatives wrt Derivatives if it contains a function.
Examples
>>> from sympy import Function, Symbol, Derivative
>>> f = Function(\'f\')
>>> x = Symbol(\'x\')
>>> Derivative(f(x),x)._diff_wrt
True
>>> Derivative(x**2,x)._diff_wrt
False'

@property
def _diff_wrt(self):

    if self.expr.is_Function:
        return True
    else:
        return False
