len() — Expert Examples

Returns the number of items in a container

EasyIntermediateAdvancedExpert

len() performance and internals

Performance characteristics and CPython implementation details.

python
# len() internals
import dis

def using_len():
    return len([1,2,3])

# Bytecode analysis
dis.dis(using_len)

# Check if it's truly built-in
import builtins
print(f"\nlen is builtin: {hasattr(builtins, 'len')}")
print(f"Type: {type(builtins.len)}")

Understanding the internal implementation helps optimize hot paths in performance-critical code.

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