How to resolve TypeError: ‘list’ object is not an iterator in Python

If you are looking for a solution to the TypeError: ‘list’ object is not an iterator error in Python, then this is the article for you. The cause of the error is that the list is used as iterator and I will fix it by passing the list. book to iter method or use generator. Post details below.

What causes the TypeError: ‘list’ object is not an iterator error?

Iterator are objects that allow us to get each element in it, which can be done iteratively. For example, using a loop over an iterator.

In Python, the iterator implements two particular protocols, the __iter__ protocol and the __next__ protocol.

• The __iter__ method returns the iterator object itself. The method must be implemented if you want to use the for loop or the print command on the iterator object.
• The __next__ method returns the next element. If the iterator runs out of elements, the program will throw a StopIteration error.

The TypeError: ‘list’ object is not an iterator error that happens because the list is used as an iterator. 

Example: 

listCities = ['Frankfurt', 'Amsterdam', 'Venice']

# Using the __next__ method causes an error
print(next(listInfor))
print(next(listInfor))
print(next(listInfor))

Output:

Traceback (most recent call last):
 File "./prog.py", line 4, in <module>
TypeError: 'list' object is not an iterator

How to solve this error?

Pass the list to the __iter__ method.

Example:

• Pass the list to the __iter__ method to get the iterator object itself. 
• The result is an iterator, this time using the __next__ method to return the next elements.

listCities = ['Frankfurt', 'Amsterdam', 'Venice']

# The __iter__ method returns the iterator object itself
iteratorObj = iter(listCities)

# Use the __next__ method to get elements in the list
print(next(iteratorObj))
print(next(iteratorObj))
print(next(iteratorObj))

Output:

Frankfurt
Amsterdam
Venice

One problem when you use the next() method is that when the iterator runs out of program elements, it will throw a StopIteration error. To prevent the program from stopping, use the try/except block.

Example:

listCities = ['Frankfurt', 'Amsterdam', 'Venice']

# The __iter__ method returns the iterator object itself
iteratorObj = iter(listCities)

try:
    # Use the __next__ method to get elements in the list
    print(next(iteratorObj))
    print(next(iteratorObj))
    print(next(iteratorObj))
    print(next(iteratorObj))
except StopIteration:
    print('Out of return value')

Output:

Frankfurt
Amsterdam
Venice
Out of return value

Use generator.

The generator is a simple way to create iterators. Without a generator, creating an iterator goes through quite a few steps, such as implementing the class with __iter()__ and __next()__ methods, keeping track of the internal conditions, keeping track of the StopIteration that occurs when no value is returned. Simplified, a Generator is a function that returns an iterator object that we can iterate over. In creating a Generator, you still use the ‘def’ keyword like a function, but instead of ‘return’ as a function, the generator uses the ‘yield’ statement to return the elements.

Example:

listCities = ['Frankfurt', 'Amsterdam', 'Venice']

def myGenerator():
    for i in range(len(listCities)):
        yield listCities[i]

gen = myGenerator()

try:
    print(next(gen))
    print(next(gen))
    print(next(gen))
    print(next(gen))
except StopIteration:
    print('Out of return value')

Output:

Frankfurt
Amsterdam
Venice
Out of return value

Summary

The problem TypeError: ‘list’ object is not an iterator in Python is probably solved. If you have any questions or have a more creative way, I hope you will share it with everyone by commenting below. Thank you for reading my article.

Jason Wilson

My name is Jason Wilson, you can call me Jason. My major is information technology, and I am proficient in C++, Python, and Java. I hope my writings are useful to you while you study programming languages.

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Name of the university: HHAU
Major: IT
Programming Languages: C++, Python, Java