Some() and Every() Equivalents With Python

Today, we’ll focus on the equivalent to JavaScript’s some and every.

The examples I provide handle both primitive values and objects.

Python Equivalent to JavaScript’s some()

Python’s equivalent of JavaScript’s some() is any().

1
2
3
4
5
6
7

# With primitives
nums = [1, 3, 5, 8, 9]
any(n % 2 == 0 for n in nums)  # True (8 is even)

# With objects
users = [{"name": "Alice", "active": False}, {"name": "Bob", "active": True}]
any(u["active"] for u in users)  # True

Python Equivalent to JavaScript’s every()

Python’s equivalent of JavaScript’s every() is all().

1
2
3
4
5
6
7

# With primitives
nums = [2, 4, 6, 8]
all(n % 2 == 0 for n in nums)  # True

# With objects
users = [{"name": "Alice", "active": True}, {"name": "Bob", "active": True}]
all(u["active"] for u in users)  # True

Performance considerations

Both short-circuit, just like their JS counterparts:

• any() stops at the first truthy result,
• all() stops at the first falsy one.

Use generator expressions (parentheses) not list comprehensions (brackets) to get the short-circuit benefit: all(x > 0 for x in data) lazily evaluates; all([x > 0 for x in data]) builds the entire list first, wasting memory and time.

A Few Caveats to Know

• With empty iterables, remember the following: any([]) returns False, all([]) returns True. This matches JavaScript behavior but catches people off guard — all([]) being True is a vacuous truth.
• No index access in Python, unlike JavaScript counterparts. If you need the index, use enumerate() like we have seen for many previous articles on this series: any(val > 10 for i, val in enumerate(data)).
• No built-in predicate parameter exists so you always need a generator expression.
• Truthiness differences between Python and JavaScript exist as the two programming languages use different falsy values. 0, "", None, [], {} are all falsy in Python. In JS, [] and {} are truthy. This matters if you’re doing bare any(items) without an explicit condition.

Credit: Photo by Pixabay on Pexels.