When you ask the interpreter to create an immutable object with a
particular value, it may at its discretion, to conserve space and
possibly conserve time, return an existing object with that same value.
This is documented somewhere in the reference.
The result of comparing two 'different' objects of the same value with
'is' depends on whether or not the interpreter used that option. And
such usage is an implementation and version specific detail. Aside from
that, the behavior of two immutable objects with the same value is
identical to that of two references to the same object. The benefits of
the optimization are considered to outweigh the cost of confusing new
Python programmers ;-)
tjr
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