I am using a python wrapper to call functions of a c++ dll library. A ctype is returned by the dll library, which I convert to numpy array
score = np.ctypeslib.as_array(score,1)
however, the array has no shape?
score
>>> array(-0.019486344729027664)
score.shape
>>> ()
score[0]
>>> IndexError: too many indices for array
How can I extract a double from the score array?
Thank you.
You can access the data inside a 0-dimensional array via indexing [()].
For example, score[()] will retrieve the underlying data in your array.
The idiom is in fact consistent:
# x, y, z are 0-dim, 1-dim, 2-dim respectively
x = np.array(1)
y = np.array([1, 2, 3])
z = np.array([[1, 2, 3], [4, 5, 6]])
# use 0-dim, 1-dim, 2-dim tuple indexers respectively
res_x = x[()] # 1
res_y = y[(1,)] # 2
res_z = z[(1, 2)] # 6
Tuples seem unnatural because you don't need to use them explicitly for the 1d and 2d cases, i.e. y[1] and z[1, 2] suffice. That option isn't available for the 0-dim case, so use the zero-length tuple.
() is a tuple with the length of 0. It's exactly the same operation as the good old array[(3, 4)].
array.item() will return a scalar regardless of how dimensions it has. np.array(0).item() == np.atleast_3d(0).item().
(), aka 0-dimensional.float(score). But how are you ending up with a 0-d array, i.e. what's the initial type and value ofscore?np.ctypeslib.as_arrayon this thing?1isn't a valid shape, and if there's only one value, why do you want to usenp.ctypeslib.as_arrayto retrieve it? Why not go through the normal ctypes interface?shapeparameter is only used for a pointer, so we knowscoreisn't initially a pointer, else passingshape=1would be an error. If you passas_arraya scalar such asc_double(-0.19), it stores an__array_interface__property on thec_doubletype withshape=(). However, in NumPy 1.8.2 this actually creates an array withshape=(1,). Maybe in older versions it creates a scalar 'array'.