How do I check if a list is empty?

python

best-practices

pythonic

efficiency

byNikita Barsukov·Oct 7, 2024

To check if a list is empty, simply use if not a:. It's a stamp of Pythonic efficiency and elegance.

Straightforward example:

# Let's cook an empty list!
pot_of_soup = [] 

# And find out whether there's soup or not!
if not pot_of_soup:  
    print("Oh no! The pot is empty!")  # A hungry programmer's nightmare! 🍲

Unpacking the magic

Python Efficiency Standards

Python loves efficiency and readability. When you use if not a:, you are not just following pythonic preference, you're leveraging Python's design principles for optimal performances. Python is optimized at the C level, making if not a: race ahead of alternatives like len(a) == 0.

Red flags and pitfalls

Coding can feel like walking through a minefield. Watch out for tricks like not not a. It might seem quicker, but it's cryptic and can cause confusion. Also, comparisons with literals like a == [] involve redundant list creation, that's like bringing a Bic lighter to a flamethrower fight!

Python vs NumPy

How about NumPy arrays? Here the rulebook changes. They're a bit like the picky eater of the Python world. They prefer their own x.size instead of our good ol' if not x: idiom. This is due to subtle differences in how boolean evaluation works in NumPy.

Coding in readable Python

Python emphasizes readability. Sticking to PEP 8 standards, if not a: is great since it’s easy to discern that the code block executes when the list is empty.

Types and sizes

When dealing with various data inputs and aiming for type consistency, numpy.asarray() should be your best buddy. It makes sure that size checks are accurate regardless of whether we're handling lists, arrays, or artist's illustrations of lists.

Embracing Python's doctrine

Pythonic checks as Zen

In the words of Paul Simon, "One man's ceiling is another man's floor." Well, in our world, that's if not a:. It's the epitome of Pythonic simplicity for checking emptiness. Remember, the guiding principle here is The Zen of Python.

Use `len()` wisely

Although len(a) == 0 is clear as a freshly cleaned window, it must be used in scenarios where precision is paramount over coding style, like cases of teaching or coding in non-Python environments.

Truth and Context

The truthiness of lists is useful across various contexts. If you're doing some house cleaning with your data, filtered_list = [item for item in a if item] comes in handy. It removes all falsey values. It's like spraying Febreze on your data!

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