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Comment by Retric | Hacker News Reader

Python’s edge cases are just as odd as every other language

  >>> a=16
  >>> a*a is a*a
  True
  >>> a=17
  >>> a*a is a*a
  False

“is”, “==“, and “=“ are all very different and none of them match their mathematical equivalents very well.

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Not really familiar with Python. Do you know why the second statement evaluates as false?

Small integer caching: https://wsvincent.com/python-wat-integer-cache/

The objects for small integers are built-in and static, but 17^2 is too big, and so new integer objects are created when the expressions are evaluated. "is" checks if two expressions represent the same object in memory. "==" checks for equality of values.

CPython keeps an array for "small value" integers (I think in the range [-5, 256]). So when Python wants 256, it'll give you a reference to the existing object. Larger numbers require a brand new object.

`is` is identity comparison and in python everything is "object". It check if two variable refer to same object (location in memory) or not. So you should not expect that `a is b` for `a=1.2 , b=1.2` be true. In this case actually first expression returned True is weird. because 0-256 objects are cached and every instance of them refer to same object.

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