Stabilizing the error with the best answers: typeerror: cannot unpack non-iterable nonetype object

Question

I'm building a new program, but when I run it, an error pops up. The error displayed is as follows:

Traceback (most recent call last):
  File "C:\Users
ehad\Desktop\Neha\Non-School\Python\Handwritten Digits 
 Recognition.py", line 38, in <module>
  X_train, y_train, X_test, y_test = load_dataset()
 TypeError: cannot unpack non-iterable NoneType object

I have tried several workarounds, but they still do not get the desired results. If you have come across this situation and have a solution for the “typeerror: cannot unpack non-iterable nonetype object” problem, pls let me know. Here is what I do:

import numpy as np
 
 
 def load_dataset():
  def download(filename, source="http://yaan.lecun.com/exdb/mnist/"):
  print ("Downloading ",filename)
  import urllib
  urllib.urlretrieve(source+filename,filename)
 
  import gzip
  
  def load_mnist_images(filename):
  if not os.path.exists(filename):
  download(filename)
  with gzip.open(filename,"rb") as f:
  data=np.frombuffer(f.read(), np.uint8, offset=16)
  
  data = data.reshape(-1,1,28,28)
  
  return data/np.float32(256)
 
  def load_mnist_labels(filename):
  if not os.path.exists(filename):
  download(filename)
  with gzip.open(filename,"rb") as f:
  data = np.frombuffer(f.read(), np.uint8, offset=8)
  return data
 
  X_train = load_mnist_images("train-images-idx3-ubyte.gz")
  y_train = load_mnist_labels("train-labels-idx1-ubyte.gz")
  X_test = load_mnist_images("t10k-images-idx3-ubyte.gz")
  y_test = load_mnist_labels("t10k-labels-idx1-ubyte.gz")
 
  return X_train, y_train, X_test, y_test
 
 
 X_train, y_train, X_test, y_test = load_dataset()
 
 
 import matplotlib
 matplotlib.use("TkAgg")
 
 import matplotlib.pyplot as plt
 plt.show(plt.imshow(X_train[3][0]))

Thanks!

hdtutoria · Accepted Answer

The cause: You get this error because X_train, y_train, X_test, y_test are defined inside in your load_mnist_images function and hence are not declared in your load_dataset function. Solution: De-indent your 5 lines from X_train = ... to return X_train, ... to fix this error.

Léa Menard · Answer

This error occurs when you attempt to perform multiple assignments to None (which, by the way, is NoneType). Take this example:

X_train, y_train, X_test, y_test = None

TypeError: cannot unpack non-iterable NoneType object

If you receive this, it is likely that you are wrong about the right-hand portion of the assignment. It is nothing.

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Stabilizing the error with the best answers: typeerror: cannot unpack non-iterable nonetype object