data = None
for i in range(1, N):
    filename = splitpath + str(i) + '.tiff'
feature = featureselection(filename)
if data is None:
    data = np.zeros((0, feature.size))
data = np.vstack((data, feature))
if data is None:
    print('no features')
else:
    print(data.shape)
Null numpy array to be appended to