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@erthalion erthalion commented Jul 23, 2015

Thanks for sharing. There is one inconsistency, which is my favorite)

In [1]: a = 1

In [2]: b = 1

In [3]: a is b
Out[3]: True

In [4]: a = 1000

In [5]: b = 1000

In [6]: a is b
Out[6]: False

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@DRMacIver DRMacIver commented Jul 23, 2015

Oh yes, that one! It gets better though:

>>> def foo():
...     a = 1000
...     b = 1000
...     return a is b
>>> foo()

The reason is that the constants used here are stored in the function object, where they're deduplicated:

>>> foo.__code__.co_consts
(None, 1000)

So inside the function both the literals are looked up as the same constant.

There is basically zero behaviour you can count on for when two numbers are going to be reference equal in Python.


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@kxepal kxepal commented Dec 16, 2015

Similar things are not always similar.

Python 3.4.3 (default, Nov 12 2015, 20:43:56) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> a, b = b'foo', b'foo'
>>> a is b
>>> a, b = 'foo', 'foo'
>>> a is b
>>> a = 'foo'
>>> b = 'foo'
>>> a is b
>>> a = b'foo'
>>> b = b'foo'
>>> a is b
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