正如numpy中常见的那样，函数版本首先确保参数是数组，然后应用方法或属性版本。

In [16]: np.ndim([[1,2,3]])
Out[16]: 2

In [17]: np.array([[1,2,3]]).ndim
Out[17]: 2

功能代码：

Signature: np.ndim(a)
Source:   
@array_function_dispatch(_ndim_dispatcher)
def ndim(a):
    """
    Return the number of dimensions of an array.

    Parameters
    ----------
    a : array_like
        Input array.  If it is not already an ndarray, a conversion is
        attempted.

    Returns
    -------
    number_of_dimensions : int
        The number of dimensions in `a`.  Scalars are zero-dimensional.

 ....
    """
    try:
        return a.ndim
    except AttributeError:
        return asarray(a).ndim
File:      c:\users\14256\miniconda3\lib\site-packages\numpy\core\fromnumeric.py
Type:      function