TypeError: 'NoneType' object is not iterable in Python

TypeError: 'NoneType' object is not iterable in Python #

The Python "TypeError: 'NoneType' object is not iterable" occurs when we try to iterate over a None value. To solve the error, figure out where the variable got assigned a None value and correct the assignment or check if the variable doesn't store None before iterating.

Here is an example of how the error occurs.

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my_list = None

# ⛔️ TypeError: 'NoneType' object is not iterable
for el in my_list:
    print(el)

We are trying to iterate over a None value and None is not iterable which causes the error.

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 a 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(['a', 'b', 'c'])


# 👇️ None
my_list = get_list()

# ⛔️ TypeError: 'NoneType' object is not iterable
for el in my_list:
    print(el)

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

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def get_list():
    return ['a', 'b', 'c']  # 👈️ return value


# 👇️ ['a', 'b', 'c']
my_list = get_list()

for el in my_list:
    print(el) # 👉️ a, b, c

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

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my_list = None

if my_list is not None:
    for i in my_list:
        print(i)
else:
    # 👇️ this runs
    print('variable stores a None value')

Alternatively, you can provide an empty list as a fallback.

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my_list = None

for i in my_list or []:
    print(i)

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

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(a):
    if len(a) > 3:
        return a


# 👇️ None
my_list = get_list(['a', 'b'])

# ⛔️ TypeError: 'NoneType' object is not iterable
for i in my_list:
    print(i)

The if statement in the get_list function is only run 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(a):
    if len(a) > 3:
        return a

    return [] # 👈️ return empty list if condition not met


# 👇️ []
my_list = get_list(['a', 'b'])

for i in my_list:
    print(i)

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

If you need to check if an object is iterable, use a try/except statement.

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my_str = 'hello'

try:
    my_iterator = iter(my_str)

    for i in my_iterator:
        print(i) # 👉️ h, e, l, l, o
except TypeError as te:
    print(te)

The iter() function raises a TypeError if the passed in value doesn't support the __iter__() method or the sequence protocol (the __getitem__() method).

If we pass a non-iterable object like a None value to the iter() function, the except block is run.

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my_list = None

try:
    my_iterator = iter(my_list)

    for i in my_iterator:
        print(i)
except TypeError as te:
    print(te)  # 👉️ 'NoneType' object is not iterable

Examples of iterables include all sequence types (list, str, tuple) and some non-sequence types like dict, file objects and other objects that define an __iter__() or a __getitem__() method.

Conclusion #

The Python "TypeError: 'NoneType' object is not iterable" occurs when we try to iterate over a None value. To solve the error, figure out where the variable got assigned a None value and correct the assignment or check if the variable doesn't store None before iterating.