How to Detect Shadowed Function Names with a Python Linter

What will you learn?

In this comprehensive guide, you will delve into utilizing a Python linter to identify instances where user-defined function names overshadow built-in function names. Mastering this skill is crucial for ensuring the clarity and reliability of your codebase.

Introduction to Problem and Solution

In the realm of Python programming, it’s common to unintentionally name our functions after built-in or globally defined functions, resulting in what is known as “shadowing.” This phenomenon can introduce unexpected behaviors in our programs as we inadvertently override default functionalities. To mitigate this issue, leveraging tools that can promptly pinpoint these conflicts is essential.

One such tool at our disposal is a linter – a utility designed to automatically scrutinize code for potential errors. In this guide, we’ll focus on harnessing flake8 along with its plugin flake8-builtins to detect shadowed function names. These tools operate by scrutinizing our code against predefined rules and conventions, highlighting any discrepancies for us to address effectively.


# Ensure you have flake8 and flake8-builtins installed:
# pip install flake8 flake8-builtins

# Content of an example Python file (
def len(list):
    return 'This is my custom function'

print(len([1, 2, 3]))

# Copyright PHD

To detect shadowing in the provided example: – Execute flake8 –install-hook=git in your terminal. – Follow up with flake8


Upon running flake8, the tool meticulously scans through the file, scrutinizing it for deviations from established coding standards. If it encounters a user-defined function bearing the same name as a built-in one (like len in our case), it raises an error:

  • A100: Possible shadowing of standard library function.

By preemptively identifying these warnings during linting before execution or deployment phases, developers can uphold code cleanliness and reduce the likelihood of bugs arising from overshadowed names.

  1. What is linting?

  2. Linting involves analyzing code using a program to uncover potential errors.

  3. Why is shadowing built-in names concerning?

  4. Shadowing built-in names can introduce confusion or unexpected behavior in your application by unknowingly overriding standard functionalities.

  5. How do I install flake8?

  6. You can install flake8 via pip: pip install flake8.

  7. Can I customize flake8 checks?

  8. Absolutely! Flake8 offers customization through configuration files where specific rules can be tailored based on your project requirements.

  9. Does flake8 solely check for naming conflicts?

  10. No, besides naming conflicts, Flake8 also inspects stylistic concerns such as line length and whitespace usage adhering to PEP 8 guidelines.

  11. Are linters obligatory?

  12. While not mandatory, linters are highly recommended as they aid in upholding high-quality standards throughout your codebase.

  13. Can I integrate flake8 into my editor/IDE?

  14. Yes! Most modern editors and IDEs provide plugins or settings facilitating seamless integration with linting tools like flake8 directly within your development environment.


Elevate your code quality by incorporating tools like linters into your workflow. By automating the detection of common pitfalls such as name shadowings early on either through command-line interaction or IDE integration, you streamline debugging processes related to overridden functions while effortlessly maintaining superior coding standards.

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