MNist loading helper for Python 2.7. For Python 3.x, see https://gist.github.com/akesling/42393ccb868125071fdea77d98a0d2f0

mnist.py

import os
import struct
import numpy as np

"""
MNist loading helper for Python 2.7.

For Python 3.x, see https://gist.github.com/akesling/42393ccb868125071fdea77d98a0d2f0

Loosely inspired by http://abel.ee.ucla.edu/cvxopt/_downloads/mnist.py
which is GPL licensed.
"""

def read(dataset = "training", path = "."):
    """
    Python function for importing the MNIST data set.  It returns an iterator
    of 2-tuples with the first element being the label and the second element
    being a numpy.uint8 2D array of pixel data for the given image.
    """

    if dataset is "training":
        fname_img = os.path.join(path, 'train-images-idx3-ubyte')
        fname_lbl = os.path.join(path, 'train-labels-idx1-ubyte')
    elif dataset is "testing":
        fname_img = os.path.join(path, 't10k-images-idx3-ubyte')
        fname_lbl = os.path.join(path, 't10k-labels-idx1-ubyte')
    else:
        raise ValueError, "dataset must be 'testing' or 'training'"

    # Load everything in some numpy arrays
    with open(fname_lbl, 'rb') as flbl:
        magic, num = struct.unpack(">II", flbl.read(8))
        lbl = np.fromfile(flbl, dtype=np.int8)

    with open(fname_img, 'rb') as fimg:
        magic, num, rows, cols = struct.unpack(">IIII", fimg.read(16))
        img = np.fromfile(fimg, dtype=np.uint8).reshape(len(lbl), rows, cols)

    get_img = lambda idx: (lbl[idx], img[idx])

    # Create an iterator which returns each image in turn
    for i in xrange(len(lbl)):
        yield get_img(i)

def show(image):
    """
    Render a given numpy.uint8 2D array of pixel data.
    """
    from matplotlib import pyplot
    import matplotlib as mpl
    fig = pyplot.figure()
    ax = fig.add_subplot(1,1,1)
    imgplot = ax.imshow(image, cmap=mpl.cm.Greys)
    imgplot.set_interpolation('nearest')
    ax.xaxis.set_ticks_position('top')
    ax.yaxis.set_ticks_position('left')
    pyplot.show()

Greys is an error, line 49 :( how to fix?

@j5scott try plt.cm.gray

sorry for asking but I am stuck on: how can I view an image using this code?

@BigHopes, after putting the unzipped files into ./mnist below my notebook this worked for me in Jupyter:

Also, to get it to work with Python 3, three changes were necessary. Add braces to line 24, xrange to range, and maybe one more thing that I now can't remember.

In order to get the show function to work you need to pass the second element of the tuple.

eg.

mnist = read("training")
image = mnist.next()

show(image[1])

---

If you are curious (like me) about how the numbers in the matrix make up the image, the function below will show that.

def ascii_show(image):
    for y in image:
         row = ""
         for x in y:
             row += '{0: <4}'.format(x)
         print row

This script is very helpful. For python3, I think we should use image = mnist.next()

Does anyone know if these functions are compatible with the EMNIST dataset? https://www.nist.gov/itl/iad/image-group/emnist-dataset

I would like to use it to parse the files but the read function keeps giving me this error:
img = img.reshape(len(lbl), rows, cols) ValueError: total size of new array must be unchanged

Full function:

def read(dataset = "training", path = "."):
    if dataset is "training":
        fname_img = os.path.join(path, 'emnist-byclass-train-images-idx3-ubyte.gz')
        fname_lbl = os.path.join(path, 'emnist-byclass-train-labels-idx1-ubyte.gz')
    elif dataset is "testing":
        pass
        fname_img = os.path.join(path, 'emnist-byclass-test-images-idx3-ubyte.gz')
        fname_lbl = os.path.join(path, 'emnist-byclass-test-labels-idx1-ubyte/gz')
    else:
        raise ValueError( "dataset must be 'testing' or 'training'")

   with open(fname_lbl, 'rb') as flbl:
        magic, num = struct.unpack(">II", flbl.read(8))
        lbl = np.fromfile(flbl, dtype=np.int8)
        print(len(lbl))
    with open(fname_img, 'rb') as fimg:
        magic, num, rows, cols = struct.unpack(">IIII", fimg.read(16))
        img = np.fromfile(fimg, dtype=np.uint8)      
        img = img.reshape(len(lbl), rows, cols)

    get_img = lambda idx: (lbl[idx], img[idx])

    for i in range(len(lbl)):
        yield get_img(i)

@krapes gunzip those gz files, it works fine with EMNIST

getting error while executing the above code:

IOErrorTraceback (most recent call last)
in ()
----> 1 train_data = list(read(dataset='training', path='.'))

in read(dataset, path)
25
26 # Load everything in some numpy arrays
---> 27 with open(fname_lbl, 'rb') as flbl:
28 magic, num = struct.unpack(">II", flbl.read(8))
29 lbl = np.fromfile(flbl, dtype=np.int8)

IOError: [Errno 13] Permission denied: '.\train-labels-idx1-ubyte'

I am facing this error,if anybody could help me with this?

in read
img = np.fromfile(fimg, dtype=np.uint8).reshape(len(lbl), rows, cols)
ValueError: cannot reshape array of size 9912406 into shape (28873,226418,1634299437)

Thanks in advance.

@Jae1015 Note that you should extract the image and label files before reading them. After extraction you should get two data files of images and labels of sizes around 47.0 MB and 60.0 kB respectively. It seems that you must have done this "Simply rename them to remove the .gz extension" but this only applies when the web browser automatically uncompress the downloaded files.

@Jae1015, the dataset in the origin website are named as 'train-labels.idx1-ubyte' . Please pay attention to the dot and the slash.

Just a notice for running under Python 3, you should change those lines:

raise ValueError("dataset must be 'testing' or 'training'") # lineno:24

for i in range(len(lbl)): # lineno:38

this script work well i think, for plotting right digit.

however, this is wired.
seems different loading tools(https://github.com/mnielsen/neural-networks-and-deep-learning/blob/master/src/mnist_loader.py) make result different for me when testing network here(https://github.com/mnielsen/neural-networks-and-deep-learning/blob/master/src/network.py).

I got this error, who can help me? Very Thanks.

raise ValueError, "dataset must be 'testing' or 'training'"

For all those who find this and want something working on Python 3.x, I've created an updated gist: https://gist.github.com/akesling/42393ccb868125071fdea77d98a0d2f0