Use all and any in Python

all(iterable) returns True if every encountered value is truthy. It returns False at the first false value. An empty iterable returns True, so validate nonempty input separately when your application requires it.

Check values or a condition

print(all([True, True]))   # True
print(all([True, False]))  # False
print(all([]))             # True

numbers = [2, 4, 6, 8]
print(all(value % 2 == 0 for value in numbers))  # True
print(all(value > 0 for value in numbers))       # True

A generator expression computes one predicate at a time and stops when the answer is known. A list comprehension evaluates every predicate before all starts, so it loses that evaluation advantage and allocates a list.

Understand truthiness

False, None, numeric zero, and empty standard containers are false. A nonempty container is normally true even if its contents are false:

print(all([1, "a", [0]]))  # True
print(all([1, "a", 0]))    # False

Custom objects can define truth testing through __bool__ or __len__. Those methods can also raise exceptions; all does not turn every failure into False.

Compare any

print(any([False, True]))  # True
print(any([]))            # False

any stops at the first truthy value. all stops at the first false value. Both consume their input as they inspect it; a partially consumed iterator continues from its current position afterward.

Validate the condition you actually need

fields = ["Alex", "alex@example.com", "  "]
complete = all(field.strip() for field in fields)
print(complete)  # False

This assumes every field is a string and rejects whitespace-only values. Plain all(fields) would accept the spaces. Neither form validates an email address or phone number; use field-specific validation for that.

For a list of test results, all(result.passed for result in results) checks the attributes. If no test results must be treated as failure, use a separate nonempty check such as bool(results) and all(...). A generator's own truth value does not reveal whether it has any elements.

FAQ

Why is all of an empty list true? There is no counterexample to the condition. That logical convention is useful, but may differ from a business rule that requires at least one record.

How is it different from and? and returns an operand, while all returns a Boolean after inspecting an iterable.

Will it finish on an infinite iterator? Only if it encounters a false value. An infinite stream of truthy values never establishes that all values are true.

References

• Python functions reference
• Python functions reference
• Python stdtypes reference