Understanding int object not iterable Error in Python for List Concatenation

Learn how to solve the `int object not iterable` error in Python when concatenating lists. Discover the right methods to add elements to your lists effectively!
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This video is based on the question https://stackoverflow.com/q/67429256/ asked by the user 'Christopher' ( https://stackoverflow.com/u/11354216/ ) and on the answer https://stackoverflow.com/a/67429290/ provided by the user 'ShadowRanger' ( https://stackoverflow.com/u/364696/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the int object not iterable Error in Python

When coding in Python, you may encounter various errors that can be puzzling, especially if you think you're implementing the correct syntax. One such error is the infamous "int object not iterable" error, particularly when you're trying to concatenate a list. Let’s break this down.

The Problem

You might find yourself trying to add numbers to a list, as shown in the following code snippet:

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In this function, the goal is to categorize numbers from number_list into two lists: over_50_list for numbers greater than or equal to 50, and under_50_list for numbers less than 50. However, users often encounter the error message stating that the "int object is not iterable", leading to confusion.

Why Does This Error Occur?

The root cause of this error comes from using the list() constructor incorrectly. Specifically, the list() function expects an iterable (like a list or a string) as an argument. However, passing a single integer does not meet that criterion — hence, the error.

Incorrect Code Example

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Here, number is an integer and cannot be converted to a list because integers are not iterable.

How to Fix It

1. Use list.append()

Instead of trying to convert an integer into a list, you should simply append the integer directly to the list. Here’s how to do that:

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This method effectively adds the number directly to over_50_list.

2. Using List Literal

If you prefer to use the + = syntax, you can create a single-element list using square brackets:

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This line is valid because [number] is a list containing a single integer, thus it is iterable.

Important Note About Initialization of Lists

Another issue is with the reinitialization of the lists. In the original code, you were redefining under_50_list and over_50_list in every iteration of the loop. This means they would always reset to empty at the beginning of each iteration.

Proper Initialization Example

To avoid this, initialize your lists outside the loop:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

When dealing with lists and individual integers in Python, remember the following:

Use list.append() to add single elements.

If you want to concatenate using + =, use list literals (e.g., [number]).

Avoid reinitializing your lists inside your loops unless you intend to start fresh on every iteration.

By applying these tips, you should be able to effectively manage your lists without running into the int object not iterable issue again. Happy coding!

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