Python all() Function

The all() function in Python checks whether all elements in an iterable are true. If they are, it returns True. Otherwise, it returns False.

Syntax

all(iterable)

Parameters:

• iterable – A list, tuple, set, dictionary, or any iterable object.

Returns:

• True – If all elements in the iterable are true (or the iterable is empty)
• False – If any element is false

Example 1: Using all() with a List of Booleans

values = [True, True, True]
print(all(values))

True

Example 2: With One False Value

values = [True, False, True]
print(all(values))

False

Example 3: Checking Numbers (Zero is False)

numbers = [1, 2, 3, 0]
print(all(numbers))

False

0 is considered False in Python.

Example 4: Empty Iterable

print(all([]))

True

This might seem strange, but in logic, a universal statement about an empty set is considered true.

Use Case: All Elements Greater Than 0

nums = [5, 8, 12, 3]
result = all(n > 0 for n in nums)
print(result)

True

Use Case: Validating All Inputs

inputs = ["name", "email", ""]
print(all(inputs))

False

This is useful in form validation — one empty string makes all() return False.

Common Mistakes

• Passing non-iterables like integers will raise a TypeError
• Assuming all() checks a condition itself — it only evaluates the truthiness of elements

Interview Tip

all() is often used with list comprehensions or generator expressions to verify conditions across a dataset.

Summary

• all() returns True only if every element is true
• 0, False, "", [], etc., are considered false
• Very useful for condition checks and validation

Practice Problem

Write a program that takes a list of ages and prints "All adults" if all are 18 or older.

ages = [22, 34, 19, 45]
if all(age >= 18 for age in ages):
    print("All adults")
else:
    print("Not all are adults")