all()

all(iterable)

Returns: bool · Updated March 13, 2026 · Built-in Functions

built-in iteration boolean validation

The all() function returns True if all elements in an iterable are truthy. It short-circuits on the first falsy value, making it efficient for checking conditions across collections.

Syntax

all(iterable)

Parameters

Parameter	Type	Default	Description
`iterable`	iterable	—	Any iterable (list, tuple, set, dict, generator, etc.)

Examples

Basic usage

# All elements are truthy
numbers = [1, 2, 3, 4, 5]
print(all(numbers))
# True

# Contains a falsy value (0)
mixed = [1, 2, 0, 4, 5]
print(all(mixed))
# False

# Empty iterable returns True
empty = []
print(all(empty))
# True

With strings

# All non-empty strings are truthy
words = ["hello", "world", "python"]
print(all(words))
# True

# Empty string is falsy
words_with_empty = ["hello", "", "world"]
print(all(words_with_empty))
# False

# Empty string itself - vacuous truth (no characters to check)
print(all(""))
# True

With dictionaries

# All keys are truthy (non-empty strings)
d = {"a": 1, "b": 2, "c": 3}
print(all(d))
# True

# Empty key is falsy
d_with_empty = {"a": 1, "": 2, "c": 3}
print(all(d_with_empty))
# False

Common Patterns

Validating user input

def validate_user(data):
    required_fields = ["username", "email", "password"]
    return all(field in data and data[field] for field in required_fields)

user = {"username": "alice", "email": "alice@example.com", "password": "secret"}
print(validate_user(user))
# True

incomplete_user = {"username": "alice", "email": "alice@example.com"}
print(validate_user(incomplete_user))
# False

Checking if all numbers are positive

numbers = [1, 2, 3, 4, 5]
all_positive = all(x > 0 for x in numbers)
print(all_positive)
# True

numbers_with_negative = [1, 2, -3, 4, 5]
all_positive = all(x > 0 for x in numbers_with_negative)
print(all_positive)
# False

Short-circuit behavior

# all() stops at the first False - useful for expensive computations
def is_valid(x):
    print(f"Checking {x}")
    return x > 0

results = [1, 2, -1, 3]
print(all(is_valid(x) for x in results))
# Checking 1
# Checking 2
# Checking -1
# False

Edge Cases

Empty iterable: Returns True (vacuous truth)
Non-iterable: Raises TypeError
None: Raises TypeError

# Empty list - returns True
print(all([]))
# True

# Raises TypeError
# all(42)  # TypeError: argument is not iterable