struct.unpack failed

[Roro]

Hello,

I am biginning coding with python and I have 2 errors I could not solve alone :

I have imported files (like MNIST\\train-images-idx3-ubyte.gz), and I try to unpack the file with the code :

import numpy as np
import gzip
import struct

def load_images(filename):
    # Open and unzip the file of images :
    with gzip.open(filename, 'rb') as f:
        # read the header, information into a bunch of variables:
        _ignored, n_images, image_columns, image_rows = struct.unpack('>IIII', bytearray)
        # read all the pixels into a long numpy array :
        all_pixels = np.frombuffer(f.read(), dtype=np.uint8)
        # reshape the array into a matrix where each line is an image:
        images_matrix = all_pixels.reshape(n_images, image_columns * image_rows)
        # Add a bias column full of 1 as the first column in the matrix
        return np.insert(images_matrix, 0, 1, axis=1)


# 60000 images, each 785 elements (1 bias + 28x28 pixels)
X_train = load_images("\\MNIST\\train-images-idx3-ubyte.gz")
X_train = load_images("\\MNIST\\t10k-images-idx3-ubyte.gz")

but it returns me these errors :

Error:
Traceback (most recent call last):
  File "recognition.py", line 23, in <module>
    X_train = load_images("\\MNIST\\train-images-idx3-ubyte.gz")
  File "recognition.py", line 13, in load_images
    _ignored, n_images, image_columns, image_rows = struct.unpack('>IIII', bytearray)
TypeError: a bytes-like object is required, not 'type'

I have tried to look at google and else, but no way to find an answer (I have just started used Python 10 days ago !).
May you help me !
Thanks

Roro noa

[deanhystad]

The error message says it wants a bytes-like object that contains the packed data. You gave it a type. What you probably want to do is read some bytes from your file and unpack the bytes you just read.

[DreamingInsanity]

On the line that's erroring (line 9), you are using struct.unpack. You are passing in "bytearray". In python bytearray is a type that an object can be.
It seems you want to unpack the header of the file. In that case you would want to read the file into a byte array and pass that in instead.
This should work:

b_array = bytearray(f.read())
_ignored, n_images, image_columns, image_rows = struct.unpack('>IIII', b_array)

EDIT: I did a quick test. For me, running that code gave me an error saying it wanted a 16 byte buffer. I had to do this instead:

_ignored, n_images, image_columns, image_rows = struct.unpack('>IIII', bytearray(a.read()[:16]))

You may need that, you may not.