Numpy has also append function to append data to array, just like append operation to list in Python. But in some cases, append in NumPy is also a bit similar to extend method in Python list. Array append Let’s first list the syntax of ndarray.append. numpy.append(arr, values, axis = None) Input Parameters parameter name type of data Description arr array_like An array to add an element values array_like Array added axis INT The axis along which values are appended.