TypeError: cannot unpack non-iterable NoneType object

TypeError: cannot unpack non-iterable NoneType object #

The Python "TypeError: cannot unpack non-iterable NoneType object" occurs when we try to unpack a None value. To solve the error, track down where the variable got assigned a None value and correct the assignment to an iterable, e.g. a list or a tuple.

Here is an example of how the error occurs.

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# ⛔️ TypeError: cannot unpack non-iterable NoneType object
a, b = None

We are trying to unpack a None value, but None values are not iterable.

If you need to declare multiple variables that store None on the same line, separate multiple None values by commas.

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a, b = None, None

print(a)  # 👉️ None
print(b)  # 👉️ None

The most common sources of None values are:

1. Having a function that doesn't return anything (returns None implicitly).
2. Explicitly setting a variable to None.
3. Assigning a variable to the result of calling a built-in function that doesn't return anything.
4. Having a function that only returns a value if certain condition is met.

Functions that don't explicitly return a value return None.

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# 👇️ this function returns None
def get_list():
    print(['one', 'two'])


# ⛔️ TypeError: cannot unpack non-iterable NoneType object
a, b = get_list()

You can use a return statement to return a value from a function.

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def get_list():
    return ['one', 'two']

a, b = get_list()

print(a)  # 👉️ 'one'
print(b)  # 👉️ 'two'

Use an if statement if you need to check whether a variable doesn't store a None value before unpacking it.

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example = None

if example is not None:
    a, b = example
else:
    # 👇️ this runs
    print('variable stores a None value')

Make sure you aren't storing the result of calling one in a variable.

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my_list = ['c', 'b', 'a']


# ⛔️ TypeError: cannot unpack non-iterable NoneType object
x, y, z = my_list.sort()

The sort functions and many other built-in functions return None because they mutate the original object.

Another common cause of the error is having a function that returns a value only if a condition is met.

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def get_list(l):
    if len(l) > 3:
        return l


my_list = get_list(['one', 'two', 'three'])
print(my_list)  # 👉️ None

# ⛔️ TypeError: cannot unpack non-iterable NoneType object
a, b, c = my_list

The if statement in the get_list function is only ran if the passed in argument has a length greater than 3.

To solve the error, you either have to check if the function didn't return None, or return a default value if the condition is not met.

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def get_list(l):
    if len(l) > 3:
        return l

    return ['', '', ''] # 👈️ return default value if condition not met


my_list = get_list(['one', 'two', 'three'])
print(my_list)  # 👉️ ['', '', '']

a, b, c = my_list

print(a, b, c)  # 👉️ "", "", ""

Now the function is guaranteed to return a value regardless if the condition is met.