not — Expert Examples

Logical NOT operator; inverts a boolean value

EasyIntermediateAdvancedExpert

not bytecode: UNARY_NOT

How 'not' compiles vs 'is not' and 'not in'.

python
import dis

def unary_not(x):
    return not x

def is_not(x):
    return x is not None

def not_in(x, y):
    return x not in y

print("not x:")
dis.dis(unary_not)
print("\nx is not None:")
dis.dis(is_not)
print("\nx not in y:")
dis.dis(not_in)

# not x -> UNARY_NOT (evaluates x, then negates)
# is not -> IS_OP 1 (single opcode, no negation step)
# not in -> CONTAINS_OP 1 (single opcode, no negation step)

'not' compiles to UNARY_NOT applied after evaluation. But 'is not' and 'not in' are single opcodes (IS_OP 1 and CONTAINS_OP 1) — they don't evaluate then negate, they do the negated comparison directly.

Want to try these examples interactively?

Open Expert Playground
← Advanced Examples