is-operator.md

is 연산자

is 는 비교하는 두 개체의 메모리 주소 값을 비교합니다. 가끔 값만을 비교하는 == 와 다른 결과를 도출하여 당황스럽게 합니다.

미묘하지만 중요한 차이점을 코드를 통해 알아봅시다.

name = 'byeongguk'
mimic = 'byeonggu'
mimic += 'k'

another_name = 'byeonggukgong'
another_mimic = 'byeonggukgong'

print(f'name: {name}, memory address: {hex(id(name))}')
print(f'mimic: {mimic}, memory address: {hex(id(mimic))}')
print(f'compare using "is": {name is mimic}, compare using "==": {name == mimic}')

print(f'another_name: {another_name}, memory address: {hex(id(another_name))}')
print(f'another_name: {another_mimic}, memory address: {hex(id(another_mimic))}')
print(f'compare using "is": {another_name is another_mimic}, compare using "==": {another_name == another_mimic}')

name: byeongguk, memory address: 0x7f78da90d530
mimic: byeongguk, memory address: 0x7f78da90d5b0
compare using "is": False, compare using "==": True

another_name: byeonggukgong, memory address: 0x10b2828f0
another_mimic: byeonggukgong, memory address: 0x10b2828f0
compare using "is": True, compare using "==": True

number = 1
mimic = 1

another_number = 257
another_mimic = 257

print(f'number: {number}, memory address: {hex(id(number))}')
print(f'mimic: {mimic}, memory address: {hex(id(mimic))}')
print(f'compare using "is": {number is mimic}, compare using "==": {number == mimic}')

print(f'anothor number: {another_number}, memory address: {hex(id(another_number))}')
print(f'another mimic: {another_mimic}, memory address: {hex(id(another_mimic))}')
print(f'compare using "is": {another_number is another_mimic}, compare using "==": {another_number == another_mimic}')

number: 1, memory address: 0x1024cbc90
mimic: 1, memory address: 0x1024cbc90
compare using "is": True, compare using "==": True

another number: 257, memory address: 0x102884f10
another number: 257, memory address: 0x102884f30
compare using "is": False, compare using "==": True

-5 ~ 256까지 파이썬이 자체적으로 정수 객체를 배열에 저장해두고 참조하기 떄문에 위와 같은 결과 값 차이를 볼 수 있습니다.

참조

큐오라, Python "is" operator?

블로그, The Hitchhiker's Guide to the Python Memory

파이썬 공식 홈페이지, PyObject* PyLong_FromLong(long v)