(self)
return self.args[0]
Returns the arbitary expression which is to have the Wavefunction
        substituted into it

        Examples
        ========

        >>> from sympy.physics.quantum.operator import DifferentialOperator
        >>> from sympy import Function, Symbol, Derivative
        >>> x = Symbol('x')
        >>> f = Function('f')
        >>> d = DifferentialOperator(Derivative(f(x), x), f(x))
        >>> d.expr
        Derivative(f(x), x)
        >>> y = Symbol('y')
        >>> d = DifferentialOperator(Derivative(f(x, y), x) +
        ...                          Derivative(f(x, y), y), f(x, y))
        >>> d.expr
        Derivative(f(x, y), x) + Derivative(f(x, y), y)
Returns the arbitary expression which is to have the Wavefunction
        substituted into it
Returns the arbitary expression which is to have the Wavefunction substituted into it
def expr(self):
        """
        Returns the arbitary expression which is to have the Wavefunction
        substituted into it

        Examples
        ========

        >>> from sympy.physics.quantum.operator import DifferentialOperator
        >>> from sympy import Function, Symbol, Derivative
        >>> x = Symbol('x')
        >>> f = Function('f')
        >>> d = DifferentialOperator(Derivative(f(x), x), f(x))
        >>> d.expr
        Derivative(f(x), x)
        >>> y = Symbol('y')
        >>> d = DifferentialOperator(Derivative(f(x, y), x) +
        ...                          Derivative(f(x, y), y), f(x, y))
        >>> d.expr
        Derivative(f(x, y), x) + Derivative(f(x, y), y)
        """

        return self.args[0]
def expr ( self ) : return self . args [ 0 ]