def ndim(x):
    """Returns the number of axes in a tensor, as an integer.

    # Arguments
        x: Tensor or variable.

    # Returns
        Integer (scalar), number of axes.

    # Examples
    ```python
        >>> from keras import backend as K
        >>> inputs = K.placeholder(shape=(2, 4, 5))
        >>> val = np.array([[1, 2], [3, 4]])
        >>> kvar = K.variable(value=val)
        >>> K.ndim(inputs)
        3
        >>> K.ndim(kvar)
        2
    ```
    """
    dims = x.get_shape()._dims
    if dims is not None:
        return len(dims)
    return None
