Save a NumPy array to disk with optional compression using 7z

save_ndarray.py

def save_ndarray(ndarray, filename, compress=False):
    """Store a single NumPy array on an .npy binary file. Tries to keep allow_pickle at False.
    Optional multithreaded compression using 7-zip (needs to be in the PATH).

    Args:
        ndarray (ndarray): Array to be stored on disk.
        filename (str): The file's name on disk. No need for .npy extension
        compress (bool, optional): Set to True to save array as .npy and then compress it to .7z

    Returns:
        None
    """
    if filename.endswith('.npy'):
        file_sans = filename[:-4]
    else:
        file_sans = filename  # String assignments are always copies!
        filename += '.npy'
    print('Saving {0!s}-array ({1:,} bytes) to disk...' .format(ndarray.shape, ndarray.nbytes))

    if compress:
        status_compression = 'compressed'
        if shutil.which('7z') is None:
            raise FileNotFoundError('7z not found on the PATH!')

        try:
            np.save(filename, ndarray, allow_pickle=False)
            status_pickle = 'unpickled'
        except ValueError:
            np.save(filename, ndarray, allow_pickle=True)
            status_pickle = 'pickled'

        subprocess.Popen('7z a ' + file_sans + '.7z ' + file_sans + '.npy -mmt', shell=True).wait()
        os.remove(filename)
        filename = file_sans + '.7z '
        print()

    else:
        status_compression = 'uncompressed'
        try:
            np.save(filename, ndarray, allow_pickle=False)
            status_pickle = 'unpickled'
        except ValueError:
            np.save(filename, ndarray, allow_pickle=True)
            status_pickle = 'pickled'

    print('Successfully saved {0!s}-array ({1:,} bytes) as [{2!s}] in [{3}], [{4}] form!'
          .format(ndarray.shape, ndarray.nbytes, filename, status_compression, status_pickle))