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Complete this python program:
def grad(func, argnum=None):
assistant
#Here is the Python program you requested.

    """Return function that computes gradient of arguments.
    Parameters
    func: a python function
    The forward (loss) function.
    argnum: an int or a list of int
    The index of argument to calculate gradient for.
    Returns
    grad_func: a python function
    A function that would compute the gradient of arguments.
    Examples
    >>> # autograd supports dynamic graph which is changed
    >>> # every instance
    >>> def func(x):
    >>>     r = random.randint(0, 1)
    >>>     if r % 2:
    >>>         return x**2
    >>>     else:
    >>>         return x/3
    >>> # use `grad(func)` to get the gradient function
    >>> for x in range(10):
    >>>     grad_func = grad(func)
    >>>     inputs = nd.array([[1, 2, 3], [4, 5, 6]])
    >>>     grad_vals = grad_func(inputs)
    """
    grad_with_loss_func = grad_and_loss(func, argnum)
    @functools.wraps(grad_with_loss_func)
    def wrapped(*args):
        return grad_with_loss_func(*args)[0]
    return wrapped