Скачать или смотреть How to Fix a Python Function That Returns None at the End

Discover how to modify your Python function to avoid returning `None` when printing even numbers from an array. This guide provides clear steps and explanations.
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This video is based on the question https://stackoverflow.com/q/74510984/ asked by the user 'Mihai Creciun' ( https://stackoverflow.com/u/20052633/ ) and on the answer https://stackoverflow.com/a/74511094/ provided by the user 'NoDakker' ( https://stackoverflow.com/u/6032177/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: Returning None in Python

When you're coding in Python, you might encounter a situation where a function is returning None unintentionally. This happens to many, especially when dealing with recursive functions. A common scenario is when you are trying to print results but then see None in your terminal output. Let's break down a specific example to understand and solve this problem.

The Example Code

Consider the following code that aims to print all even numbers from an array:

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

This code should effectively print the even numbers, but it also outputs None at the end. The confusion arises from the fact that the evenlis function is being called within a print() statement.

Analyzing the Output

When the function evenlis(arr) is invoked inside print(), its return value is what gets printed. In our case, since the function has no explicit return statement providing a value (other than None), Python outputs None after the even numbers.

The Solution: Modifying the Function Call

To resolve this issue, we can separate the function call from the print statement. Here’s a simple way to make the change:

Step-by-Step Fix

Remove the print() around the function call.
Instead of using print(evenlis(arr)), we can call the function directly:

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

Print a newline afterward.
We can add a print() statement after the function call to move our cursor to a new line, ensuring the output remains clean:

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

Updated Code

Here’s how your updated code would look like after the modifications:

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Output

With this change, when you run the program, you should see the following output:

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

This solution elegantly addresses the None problem and allows you to print the even numbers without disrupting the flow of your Python program.

Conclusion

Encountering a None output in your Python functions can be perplexing, especially when you're only trying to display values. By simply separating the function call from the print statement, you can avoid this issue altogether. Now, you can focus on implementing and improving your functions without the hassle of unwanted output.

Make sure to apply this change in your future code, and happy coding!