PythonCommunity question

a is b True for 256 but False for 257??

Asked by Fatima Siddiqui 1 month ago 2 answers 10 votes

>>> a = 256
>>> b = 256
>>> a is b
True
>>> a = 257
>>> b = 257
>>> a is b
False

what

2 answers

aman khan1 month agoMost voted8

CPython keeps cached int objects from -5 to 256, so every 256 is the same object. 257 gets created fresh each time in the REPL.

If you put the same code in a .py file it might print True for 257 too, because constants in one code block get reused.

Use == for values, `is` only for None.

Fatima Siddiqui1 month ago1

REPL vs file giving different answers is crazy

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