Issue with `mypy: type[list[Any]]` and attribute “__iter__”

What will you learn?

In this tutorial, you will learn how to resolve the error message “mypy: type[list[Any]] has no attribute ‘__iter__’ (not iterable)” in Python. We will explore common scenarios where this error occurs and provide solutions to ensure proper iteration over objects.

Introduction to the Problem and Solution

Encountering the error message “mypy: type[list[Any]] has no attribute ‘__iter__’ (not iterable)” indicates an attempt to iterate over a type annotation rather than an actual list object in Python. This commonly happens when using tools like mypy for static typing checks. To address this issue effectively, it is essential to work with concrete list instances instead of just type hints.

By understanding how to handle iterable objects correctly, we can prevent such errors and ensure smooth execution of our code. Proper instantiation of data structures is crucial for seamless iteration operations, especially when dealing with nested lists or custom classes that require iteration support.


# Ensure working with actual list instances for iteration purposes
my_list: list[int] = [1, 2, 3]
for item in my_list:

# Handle nested lists or complex structures properly
nested_list: list[list[int]] = [[1, 2], [3, 4]]
for sublist in nested_list:
    for num in sublist:

# Implement __iter__() method for custom classes or types requiring iteration support

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# Copyright PHD


In the provided code snippet: – Declare a concrete list my_list containing integers and iterate over its elements. – Manage a nested list nested_list, ensuring correct iteration through each sublist. – Proper instantiation of data structures before iterating is emphasized. – For custom classes or types needing iteration support, implementing the __iter__() method enables seamless usage in loops.

    Why am I getting the error “mypy: type[list[Any]] has no attribute ‘__iter__'”?

    This error arises from attempting to iterate over a type hint instead of an actual list object. Verify proper assignment of values to variables.

    How do I fix the “‘list’ object is not callable” error while iterating over lists?

    Ensure correct syntax by directly looping through list elements without adding unnecessary parentheses.

    Can sets or dictionaries be iterated similarly like lists?

    Yes, sets and dictionaries support iteration methods (set.__iter__(), dict.__iter__()) facilitating element traversal efficiently using loops.

    Can user-defined classes be made iterable?

    Certainly! By implementing special methods like __iter__() and __next__(), custom classes can exhibit iterator behavior too.

    What if my function returns a generator instead of a regular list?

    Generators can be iterated upon akin to lists but require accessing elements differently due to their lazy evaluation nature using functions like next() or within comprehension constructs.

    Does implicit vs explicit conversion impact iterating through different data types?

    Implicit conversions done automatically by Python may affect iterations as certain types may not inherently support being looped over unless explicitly cast into suitable iterable forms beforehand.

    Are there specific considerations when handling asynchronous iterators during iterations?

    Asynchronous iterators offer enhanced capabilities but require appropriate use of async/await keywords along with async-based constructs for efficient non-blocking operations during iterations within asyncio environments.


    Resolving issues related to incorrect iteration involves ensuring proper instantiation of data structures and understanding iterator mechanisms in Python. By adhering to best practices outlined here and utilizing syntax conventions tailored to your specific needs within your codebase, you can achieve smoother execution without encountering unexpected errors related to iterable attributes.

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