Cannot unpack non iterable nonetype object ошибка

I know this question has been asked before but I can’t seem to get mine to work.

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]))

This is the error I am getting:

Traceback (most recent call last):
  File "C:UsersnehadDesktopNehaNon-SchoolPythonHandwritten 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 am new to machine learning. Did I just miss something simple? I am trying a Handwritten Digit Recognition project for my school Science Exhibition.

In Python, you can unpack iterable objects and assign their elements to multiple variables in the order that they appear. If you try to unpack a NoneType object, you will throw the error TypeError: cannot unpack non-iterable NoneType object. A NoneType object is not a sequence and cannot be looped or iterated over.

To solve this error, ensure you do not assign a None value to the variable you want to unpack. This error can happen when calling a function that does not return a value or using a method like sort(), which performs in place.

This tutorial will go through the error in detail and an example to learn how to solve it.

TypeError: cannot unpack non-iterable NoneType object

What is a TypeError?

TypeError occurs in Python when you perform an illegal operation for a specific data type. NoneType is the type for an object that indicates no value. None is the return value of functions that do not return anything. Unpacking is only suitable for iterable objects,

What is Unpacking in Python?

Unpacking is the process of splitting packed values into individual elements. The packed values can be a string, list, tuple, set or dictionary. During unpacking, the elements on the right-hand side of the statement are split into the values on the left-hand side based on their relative positions. Let’s look at the unpacking syntax with an example:

values = [40, 80, 90]

x, y, z = values

print(f'x: {x}, y: {y}, z: {z}')

The above code assigns the integer values in the value list to three separate variables. The value of x is 40, y is 80, and the value of z is 90. Let’s run the code to get the result:

x: 40, y: 80, z: 90

You can also unpack sets and dictionaries. Dictionaries are only ordered for Python version 3.7 and above but are unordered for 3.6 and below. Generally, it is not recommended to unpack unordered collections of elements as there is no guarantee of the order of the unpacked elements.

You cannot unpack a None value because it is not an iterable object, and an iterable is a Python object that we can use as a sequence. You may encounter this error by unpacking the result from a function that does not have a return statement.

Example

Let’s look at an example of a list of weights in kilograms that we want to sort and then unpack and print to the console.

# List of weights

weights = [100, 40, 50]

# Sort the list

weights = weights.sort()

# Unpack

a, b, c = weights

# Print Values to Console

print('Light: ', a)

print('Medium: ', b)

print('Heavy: ', c)

Let’s run the code to see the result:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
      9 # Unpack
     10 
---≻ 11 a, b, c = weights
     12 
     13 # Print Values to Console

TypeError: cannot unpack non-iterable NoneType object

The program throws the error because the sort() method sorts the list of weights in place and returns None. However, we assigned the result of sort() to the variable weights, so when we try to unpack weights, we attempt to unpack a None value, which is not possible.

Solution

To solve the error, we need to ensure we are not assigning a None value to the list variable weights. Let’s look at the revised code:

# List of weights

weights = [100, 40, 50]

# Sort the list

weights.sort()

# Unpack

a, b, c = weights

# Print Values to Console

print('Light: ', a)

print('Medium: ', b)

print('Heavy: ', c)

Instead of assigning the sort() function result to the weights variable, we sort the list in place. Let’s run the code to see what happens:

Light:  40
Medium:  50
Heavu:  100

The program successfully sorts the list of weights and unpacks them into three variables, and prints the values to the console.

Summary

Congratulations on reading to the end of this tutorial. The NoneType object is not iterable, and when you try to unpack it, we will throw the error: “TypeError: cannot unpack non-iterable NoneType object”. A common cause of this error is when you try to unpack values from a function that does not return a value. To solve this error, ensure that the value you attempt to unpack is a sequence, such as a list or a tuple.

For more reading on what you can do with iterable objects go to the article called: How to Use the Python Map Function.

For more reading on cannot unpack non-iterable object errors, go to the articles:

• How to Solve Python TypeError: cannot unpack non-iterable int object
• How to Solve Python TypeError: cannot unpack non-iterable float object

Go to the online courses page on Python to learn more about Python for data science and machine learning.

Have fun and happy researching!

The TypeError: cannot unpack non-iterable NoneType object occurs when we try to unpack the values from the method that does not return any value or if we try to assign the None value while unpacking the iterables.

In this tutorial, we will look into what exactly is TypeError: cannot unpack non-iterable NoneType object and how to resolve the error with examples.

What is Unpacking in Python?

In Python, the function can return multiple values, and it can be stored in the variable. This is one of the unique features of Python when compared to other languages such as C++, Go Java, C#, etc. 

Unpacking in Python is an operation where an iterable of values will be assigned to a tuple or list of variables.

Example of List Unpacking

x,y,z = [5,10,15]
print(x)
print(y)
print(z)

Output

5
10
15

First, let us see how to reproduce this issue and why developers face this particular issue with a simple example.

# list of cars
my_cars = ["Ford", "Audi", "BMW"]

# sort the cars in Alphabetical Order
my_cars = my_cars.sort()

# unpack cars into different variables
a, b, c = my_cars

print("Car", a)
print("Car", b)
print("Car", c)

Output

Traceback (most recent call last):
  File "c:PersonalIJSCodecode22.py", line 8, in <module>
    a, b, c = my_cars
TypeError: cannot unpack non-iterable NoneType object

In the above example, we have a simple list, and we are sorting the list in alphabetical order and then unpacking them into different variables.

The sort() function sorts the elements in alphabetical order by modifying the same object and does not return any value. The return type will be considered as None value.

The sort() method returns None value and here we are assigning the None value to the my_cars variable.

We are unpacking the None value into each of these variables, which results in  TypeError: cannot unpack non-iterable NoneType object

The same can happen when we use the user-defined function, which returns the None Value or if you have forgotten the return statement inside your function. In simple terms, any method that does not return a value or if it returns the value of None will lead to this error.

How to resolve TypeError: cannot unpack non-iterable NoneType object

We can resolve the cannot unpack non-iterable NoneType object by ensuring the unpacked items does not contain None values while assigning to the variables.

Let us see the various scenarios and the solutions for each scenario.

Scenario 1: Unpacking iterables with built-in methods

In the case of unpacking iterables we need to ensure that we are not using any built-in methods that return None while assigning it to variables.

In our above example, we have used the sort() method, which returns None value, and because of it, we get the TypeErrror.

As shown below, we can resolve the issue by first sorting the list and then unpacking the items. We have not assigned the None value to any variable here. The sort() doesn’t return any value however it modifies the original list into alphabetical order here. Hence unpacking the list works as expected in this case.

# list of cars
my_cars = ["Ford", "Audi", "BMW"]

# sort the cars in Alphabetical Order
my_cars.sort()

# unpack cars into different variables
a, b, c = my_cars

print("Car", a)
print("Car", b)
print("Car", c)

Output

Car Audi
Car BMW
Car Ford

.

Scenario 2: Unpacking user-defined function which returns multiple values

If you have written a custom function that returns multiple values, you need to ensure that the return value should not be of None value while unpacking the items.

Also, we need to ensure that the function has a proper return statement defined; else, it could also lead to the TypeError: cannot unpack non-iterable NoneType object.

def custom_function(a, b):
    return a

x, y = custom_function(5, 10)
print(x)
print(y)

Output

Traceback (most recent call last):
  File "c:PersonalIJSCodecode22.py", line 5, in <module>
    x, y = custom_function(5, 10)
TypeError: cannot unpack non-iterable int object

Solution

Here we need to return both a and b with proper values as we are unpacking 2 items. If any of it is None or if we do not return 2 values then you will get an TypeError exception again.

def custom_function(a, b):
    return a,b

x, y = custom_function(5, 10)
print(x)
print(y)

Output

5
10

Conclusion

The TypeError: cannot unpack non-iterable NoneType object occurs when we try to unpack the values from the method that returns multiple values as None value or if we try to assign the None value while unpacking the iterables.

We can resolve the issue by ensuring the function has a proper return statement. 

Also, when we try to unpack the values from a method and assign the values to the variables, we need to make sure the values are not of type None.