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pythoninfinity

Why does float('Inf') is float('Inf') returns false in Python?

Whilst reading about Python's infinity, I came accross this :

>>>float('Inf') == float('Inf')
True
>>>float('Inf') is float('Inf')
False
>>>float('Inf') is not float('Inf')
True

I understand that equals works but I am wondering what float('Inf') actually points to that make the is test return False ? Is it different each time you call float('Inf') ?

EDIT: I am not asking about the difference between == and is. I am asking about the implementation details of float('Inf') and the nature of this object.

Solution

  • is and == in python are quite different. is checks for identity while == checks for equality as some other users have already stated here:Is there a difference between == and is in Python?

    float() creates (or might create, depending on your interpreter) a new object which is not identical (but is equal) to another object created by float() having the same argument.

    Cpython may return a True for your check, but other VMs or interpreters may not as described by Microsoft

    So:

     >>> float(2) is float(2)
 >>> False
 >>> float(2) == float(2)
 >>> True

    In fact their identities can be seen as completely different using id()

     >>> id(float(2))
 >>> 251452
 >>> id(float(2)) # same call
 >>> 251934       # different result

    So you should only use is if you really, really want to test for identity and not value.