len()

Syntax

len(object)

Examples

print(len("Hello"))              # 5
print(len([1, 2, 3, 4]))         # 4
print(len((1, 2)))               # 2
print(len({"a": 1, "b": 2}))     # 2 (counts key-value pairs)
print(len({1, 2, 3}))            # 3

cart = []

if len(cart) == 0:
    print("Your cart is empty")

password = "abc123"
if len(password) < 8:
    print("Password must be at least 8 characters")

fruits = ["apple", "banana", "cherry"]

for i in range(len(fruits)):
    print(f"{i}: {fruits[i]}")

# Often cleaner with enumerate()
for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

Best practices

• Prefer 'if not cart:' over 'if len(cart) == 0:' for checking emptiness - it's more idiomatic and works for any falsy check
• Use enumerate() instead of range(len(...)) when you need both index and value while looping
• len() works on any object that implements __len__, including custom classes you define yourself
• len() raises a TypeError on objects that don't have a defined length, like integers or None

At a glance

Purpose

Scripting and general-purpose applications

File extension

.py

Runs in

Python interpreter

Usually used with

Python standard library and packages

Specifications & further reading

• Python language reference

Related Python documentation