median(a, 
axis=None, 
out=None,
overwrite_input=False, 
keepdims=False)

> a = np.array([[10, 7, 4], [3, 2, 1]])
> a
array([[10, 7, 4],
    [ 3, 2, 1]])
> np.median(a)
3.5
> np.median(a, axis=0)
array([ 6.5, 4.5, 2.5])
> np.median(a, axis=1)
array([ 7., 2.])
> m = np.median(a, axis=0)
> out = np.zeros_like(m)
> np.median(a, axis=0, out=m)
array([ 6.5, 4.5, 2.5])
> m
array([ 6.5, 4.5, 2.5])
> b = a.copy()
> np.median(b, axis=1, overwrite_input=True)
array([ 7., 2.])
> assert not np.all(a==b)
> b = a.copy()
> np.median(b, axis=None, overwrite_input=True)
3.5