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How to Use Python Lambda Functions

Emmanuel Oyibo on February 21, 2024

This in-depth tutorial will teach you how to use Python Lambda functions. You’ll understand why they help simplify code in the context of functiona...
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Pierre Gradot • • Edited

Cool article.

Note however that lambdas in your list comprehension examples are probably useless:

>>> numbers = [1, 2, 3, 4, 5, 6]

>>> [(lambda x: x * 2)(x) for x in numbers]
[2, 4, 6, 8, 10, 12]

>>> [x * 2 for x in numbers]
[2, 4, 6, 8, 10, 12]
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Emmanuel Oyibo • • Edited

You're absolutely right! In this specific case, the list comprehension version [x * 2 for x in numbers] is more concise and readable. Thanks for pointing that out.

However, I want to emphasize that my article aims to introduce beginners to the concept of lambda functions. Using them in list comprehensions, even in relatively straightforward cases, can help solidify understanding. It prepares readers to recognize scenarios where lambdas offer a unique advantage, such as with custom sorting or more complex inline transformations.

Do you have examples where you feel lambdas provide an undeniable benefit within list comprehensions?

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Pierre Gradot • • Edited

I can't think of any good example. And for a good reason: see the documentation docs.python.org/3/tutorial/datastr... and in particular the snippets 2 and 3 in this section. A list comprehension is probably already a syntax sugar to avoid writing a lambda.

It prepares readers to recognize scenarios where lambdas offer a unique advantage

My advice would be then to show cases where lambdas are not useful, and explicitly mention it.

pylint has a special warning about lambdas: pylint.pycqa.org/en/latest/user_gu...

For instance:

numbers = [1, 2, 3, 4, 5, 6]
doubled_numbers = [(lambda x: x * 2)(x) for x in numbers]
print(doubled_numbers)
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Analysis:

% python -m pylint main.py                
************* Module main
main.py:1:0: C0114: Missing module docstring (missing-module-docstring)
main.py:2:19: C3002: Lambda expression called directly. Execute the expression inline instead. (unnecessary-direct-lambda-call)

------------------------------------------------------------------
Your code has been rated at 3.33/10 (previous run: 6.67/10, -3.33)
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Note also that pylint discourages to save a lambda to a variable: pylint.readthedocs.io/en/stable/us...

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Emmanuel Oyibo •

Thank you for your detailed feedback and the links to both the Python documentation and the Pylint guidelines! I really appreciate you sharing your insights.

You're right that the tradeoffs between lambda functions and list comprehensions, especially for beginners, are worth a closer look. I'll definitely consider adding a section to my article that explicitly discusses these tradeoffs and where the Pylint guidance would steer programmers away from lambdas.

Thank you, once again.

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Pierre Gradot •

Glad if you've learned something :)

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