gradient.py 文件源码

def grad_not_implemented(op, x_pos, x, comment=""):
    """
    Return an un-computable symbolic variable of type `x.type`.

    If any call to tensor.grad results in an expression containing this
    un-computable variable, an exception (NotImplementedError) will be
    raised indicating that the gradient on the
    `x_pos`'th input of `op` has not been implemented. Likewise if
    any call to theano.function involves this variable.

    Optionally adds a comment to the exception explaining why this
    gradient is not implemented.
    """

    return (NullType((
        "This variable is Null because the grad method for "
        "input %s (%s) of the %s op is not implemented. %s"
    ) % (x_pos, x, op, comment)))()