[Python-Dev] Clean way in python to test for None, empty, scalar, and list/ndarray? A prayer to the gods of Python (original) (raw)

Robert Kern robert.kern at gmail.com
Fri Jun 14 22:20:50 CEST 2013

On 2013-06-14 21:03, Brett Cannon wrote:

On Fri, Jun 14, 2013 at 3:12 PM, Martin Schultz <maschu09 at gmail.com_ _<mailto:maschu09 at gmail.com>> wrote:

- add a size attribute to all objects (I wouldn't mind if this is None in case you don't really know how to define the size of something, but it would be good to have it, so that anything.size would never throw an error

This is what len() is for. I don't know why numpy doesn't define the len method on their array types for that.

It does. It gives the size of the first axis, i.e. the one accessed by simple indexing with an integer: some_array[i]. The size attribute givens the total number of items in the possibly-multidimensional array. However, one of the other axes can be 0-length, so the array will have no elements but the length will be nonzero.

[~] |4> np.empty([3,4,0]) array([], shape=(3, 4, 0), dtype=float64)

[~] |5> np.empty([3,4,0])[1] array([], shape=(4, 0), dtype=float64)

[~] |6> len(np.empty([3,4,0])) 3

-- Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco

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